Bis(tetramethylcyclopentadienyl)titanium chemistry. Molecular structures of [(C5HMe4)(μ-η1:η5-C 5Me4)Ti]2 and [(C5HMe4)2Ti]2N2

Article abstract of DOI:10.1021/om960509w

Thermolysis of bis(tetramethylcyclopentadienyl)-stabilized titanium(III) compounds (C₅-HMe₄)₂TiR (R = Me (2), Ph (3)) yields, in marked contrast with the bis(pentamethylcyclopentadienyl) analog, the dimeric product [(C₅HMe₄)(μ-η¹:η⁵-C ₅Me₄)Ti]₂ (4), with a bridging metalated tetramethylcyclopentadienyl ligand. The hydride (C₅HMe₄)₂TiH (5), synthesized by hydrogenolysis of 2 or 3, reacts with N₂ to form the dinuclear Ti(II) dinitrogen compound [(C₅HMe₄)₂Ti]₂N₂ (8). Under a dynamic vacuum, the dinitrogen complex 8 loses the N₂ ligand to give the titanocene (C₅HMe₄)₂Ti (10). The molecular structures of both 4 and 8 were determined by X-ray diffraction methods.

Full text of DOI:10.1021/om960509w

Organometallics 1996, 15, 4977-4983
4977
Bis(tetr a m eth ylcyclop en ta d ien yl)tita n iu m Ch em istr y.
Molecu la r Str u ctu r es of [(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 a n d
[(C5HMe4)2Ti]2N2
J eannette M. de Wolf,† Rolf Blaauw,† Auke Meetsma,† J an H. Teuben,*,†
Robert Gyepes,‡ Vojtech Varga,‡ Karel Mach,*,‡ Nora Veldman,§ and
Anthony L. Spek§
Groningen Center for Catalysis and Synthesis, Department of Chemistry, University of
Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands, J . Heyrovsky´ Institute of
Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejsˇkova 3, 182 23 Prague
8, Czech Republic, and Bijvoet Center for Biomolecular Research, Crystal and Structure
Chemistry, Utrecht University, Padualaan 8, 3584 CH Utrecht, The Netherlands
Received J une 25, 1996X
Thermolysis of bis(tetramethylcyclopentadienyl)-stabilized titanium(III) compounds (C5-
HMe4)2TiR (R ) Me (2), Ph (3)) yields, in marked contrast with the bis(pentamethylcyclo-
pentadienyl) analog, the dimeric product [(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 (4), with a bridging
metalated tetramethylcyclopentadienyl ligand. The hydride (C5HMe4)2TiH (5), synthesized
by hydrogenolysis of 2 or 3, reacts with N2 to form the dinuclear Ti(II) dinitrogen compound
[(C5HMe4)2Ti]2N2 (8). Under a dynamic vacuum, the dinitrogen complex 8 loses the N2 ligand
to give the titanocene (C5HMe4)2Ti (10). The molecular structures of both 4 and 8 were
determined by X-ray diffraction methods.
6
In tr od u ction
and (C5Me5)2TiCl2 (4.0°) is larger than between the
7
former and unsubstituted (C5H5)2TiCl2 (2.4°). In the
Methyl substituents at cyclopentadienyl ligands influ-
ence the reactivity of metallocene derivatives by their
electron-donating effect and by steric shielding of the
central atom.1 The electron-donating effect leads to an
increased electron density at the cyclopentadienyl ligand
and, consequently, at the metal atom.2 Experimentally,
this is observed as a decreased ionization potential of
both the dominantly Cp′ (Cp′ ) C5H5-nMen, n ) 0-5)
molecular orbitals and the dominantly metal orbitals.3
UPS spectra of the titanocene dihalides Cp′2TiX2 and
monohalides Cp′2TiX (X ) Cl, Br) show an approxi-
mately constant increase in energy of the π(Cp′) and
d(Ti) orbitals per methyl group.3e,f The additivity of the
effect of methylation on the ionization energies does not
extend to the pentamethylcyclopentadienyl derivatives
of the dihalide compounds,3e probably as a result of the
larger CE-Ti-CE (CE ) Cp ring centroid) angle
affecting the orbital energies.4 Structure data show that
Ti(III) series Cp′2TiCl, the difference in the CE-Ti-
8
5
CE angle between the C5Me5 and the C5HMe4 com-
pound is 4.5°.9 The molecular structures of (C5HMe4)2-
TiXn (n ) 1, X ) Cl, I and n ) 2, X ) Cl) compounds
show that the C5HMe4 ligands are staggered with the
unsubstituted carbon atoms of each Cp ring in hinge
positions.5 With five instead of four methyl substituents
on the Cp ring, steric repulsion between the methyl
groups in hinge positions is relieved by opening up the
Cp′2Ti wedge, leading to the above-mentioned increase
in the CE-Ti-CE angle.
The number of methyl substituents on the cyclopen-
tadienyl rings of titanocene compounds has a profound
effect on their reactivity. In the series Cp′2TiX (X )
Cl, Br, I), the number of methyl substituents determines
whether the compound is monomeric or dimeric. The
C5H5 and C5H4Me derivatives form dimers with bridging
halide ligands, both in the solid state10a and in solution.10b
In polar solvents they split to give monomeric
solvates.10c,11 Recently, the 1,3-dimethylcyclopentadi-
enyl complex [(C5H3Me2)2Ti(µ-Cl)]2 was found to behave
5
the difference in this angle between (C5HMe4)2TiCl2
† University of Groningen.
‡ Academy of Sciences of the Czech Republic.
§ Utrecht University.
X Abstract published in Advance ACS Abstracts, October 1, 1996.
(1) (a) Thompson, M. E.; Bercaw, J . E. Pure Appl. Chem. 1984, 56,
1-11. (b) Watson, P. L.; Parshall, G. W. Acc. Chem. Res. 1985, 18,
51-56. (c) Calabro, D. C.; Hubbard, J . L.; Blevins, C. H., II; Campbell,
A. C.; Lichtenberger, D. L. J . Am. Chem. Soc. 1981, 103, 6839-6846.
(2) (a) Robbins, J . L.; Edelstein, N.; Spencer, B.; Smart, J . C. J . Am.
Chem. Soc. 1982, 104, 1882-1893 and references therein. (b) Miller,
E. J .; Landon, S. J .; Brill, T. B. Organometallics 1985, 4, 533-538.
(3) (a) Lichtenberger, D. L.; Kellogg, G. E. Acc. Chem. Res. 1987,
20, 379-387. (b) Petersen, J . L.; Lichtenberger, D. L.; Fenske, R. F.;
Dahl, L. F. J . Am. Chem. Soc. 1975, 97, 6433-6441. (c) Cauletti, C.;
Clark, J . P.; Green, J . C.; J ackson, S. E.; Fragala, I. L.; Ciliberto, E.;
Coleman, A. W. J . Electron Spectrosc. Relat. Phenom. 1980, 18, 61-
73. (d) Condoreli, G.; Fragala, I. L.; Centineo, A.; Tondello, E. J .
Organomet. Chem. 1975, 87, 311-315. (e) Vondra´k, T.; Mach, K.;
Varga, V. J . Organomet. Chem. 1989, 367, 69-76. (f) Vondra´k, T.;
Mach, K.; Varga, V. Organometallics 1992, 11, 2030-2034.
(4) Lauher, J . W.; Hoffmann, R. J . Am. Chem. Soc. 1976, 98, 1729-
1742.
(5) Troyanov, S. I.; Rybakov, V. B.; Thewalt, U.; Varga, V.; Mach,
K. J . Organomet. Chem. 1993, 447, 221-225.
(6) McKenzie, T. C.; Sanner, R. D.; Bercaw, J . E. J . Organomet.
Chem. 1975, 102, 457-466.
(7) Clearfield, A.; Warner, D. K.; Saldarriaga-Molina, C. H.; Ropal,
R.; Bernal, I. Can. J . Chem. 1975, 53, 1622-1629.
(8) Pattiasina, J . W.; Heeres, H. J .; Van Bolhuis, F.; Meetsma, A.;
Teuben, J . H.; Spek, A. L. Organometallics 1987, 6, 1004-1010.
(9) Comparison of the CE-Ti-CE angles for bis(cyclopentadienyl)-
derivatives Cp′2TiCl (Cp′ ) C5H5-nMen) with various degrees of methyl
substitution is hampered by the fact that for n ) 0, 1 the compounds
are dimers,10a thus adding the steric interaction between the two Cp′2-
Ti fragments as a new variable to determine the CE-Ti-CE angle.
(10) (a) J ungst, R.; Sekutowski, D.; Davis, J .; Luly, M.; Stucky, G.
Inorg. Chem. 1977, 16, 1645-1655. (b) Coutts, R. S. P.; Wailes, P. C.;
Martin, R. L. J . Organomet. Chem. 1973, 47, 375-382. (c) Samuel,
E.; Vedel, J . Organometallics 1989, 8, 237-241. (d) Mach, K.; Varga,
V.; Schmid, G.; Hiller, J .; Thewalt, U. Collect. Czech. Chem. Commun.,
in press.
S0276-7333(96)00509-2 CCC: $12.00 © 1996 American Chemical Society

4978 Organometallics, Vol. 15, No. 23, 1996
de Wolf et al.
analogously.10d The Cp′2TiX compounds with n ) 3-5
are monomeric.5,8,11 Dimeric “titanocene”, synthesized
by reduction of (C5H5)2TiCl2 with LiAlH4, contains two
bridging hydrides and a bridging fulvalene ligand.12
Similar compounds can be obtained for cyclopentadienyl
ligands up to a maximum of three methyl substituents,13
whereas for C5HMe4 two adjacent methyl groups are
metalated and a new cyclopentadienyl-type ligand is
formed, resulting in {µ-η3:η4-C5H(CH3)2(CH2)2}{(C5-
HMe4)Ti(µ-H)}2 with a bridging µ-η3:η4-1,4-dimethyl-2,3-
dimethylenecyclopentadienyl ligand.14 For the penta-
methylcyclopentadienyl derivatives (C5Me5)2TiR, ther-
molysis ultimately gave analogous dimetalation of a
cyclopentadienyl ligand, but here the monomeric com-
pound (C5Me5)(η3:η4-C5(CH3)3(CH2)2)Ti15 with a tri-
methyl-1,2-dimethylenecyclopentadienyl ligand was ob-
tained as the main product.16
F igu r e 1. ORTEP drawing (50% probability level) and
atom-labeling scheme for [(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 (4).
Hydrogen atoms are omitted for clarity.
In this article we compare reactivity differences of
tervalent titanium compounds Cp′2TiR (R ) Me, Ph, H)
in relation to the stabilizing cyclopentadienyl (C5HMe4
vs C5Me5) ligand system.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for [(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 (4)
Ti1-C1
Ti1-C2
Ti1-C3
Ti1-C4
Ti1-C5
Ti1-CE1a
Ti1-C5a
2.320(2)
2.435(2)
2.434(2)
2.325(2)
2.284(2)
2.0231(9)
2.193(2)
Ti1-C10
Ti1-C11
Ti1-C12
Ti1-C13
Ti1-C14
Ti1-CE2a
2.360(2)
2.431(2)
2.430(2)
2.365(2)
2.311(2)
2.0515(9)
Resu lts a n d Discu ssion
Th er m olysis of (C5HMe4)2TiMe (2) an d (C5HMe4)2-
TiP h (3). Compounds 2 and 3 were synthesized by salt
metathesis reactions of (C5HMe4)2TiCl (1) with MeLi
and PhMgBr, respectively, in analogy with the synthesis
of (C5Me5)2TiR compounds.17 The compounds are para-
magnetic, which complicates NMR spectroscopic char-
acterization. 1H NMR spectroscopy shows two reso-
nances for the ring methyl groups, one very broad signal
at 48 ppm for 2 and at 40 ppm for 3 and a much
narrower resonance (3.0 ppm (2) and 4.1 ppm (3)). The
Ti-Me group of compound 2 appears at -26 ppm.18 To
facilitate identification, 2 and 3 were oxidized with
PbCl2,19 yielding the diamagnetic (C5HMe4)2Ti(Me)Cl
and (C5HMe4)2Ti(Ph)Cl, respectively. Thermolysis of 2
or 3 in toluene at 130 °C led to formation of a green-
brown crystalline compound, which is poorly soluble in
organic solvents, thereby precluding proper character-
ization by NMR spectroscopy. To¨pler pump experi-
ments revealed that 1 equiv of CH4/Ti is released during
thermolysis of 2. Evolution of benzene was observed
during thermolysis of the phenyl complex 3 (GC). An
X-ray crystal structure determination showed that the
dimeric product [(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 (4) had
been formed (eq 1), which is in marked contrast with
the monomeric fulvene complex (C5Me5)(η1:η5-C5Me4-
Ti1-C5-Ti1a
CE1-Ti1-CE2
104.62(8)
141.43(2)
C5-Ti1-C5a
75.38(7)
a
CE1 ) C1-C5 ring centroid; CE2 ) C10-C14 ring centroid.
CH2)Ti, the product of the thermolysis of the penta-
methylcyclopentadienyl analog (C5Me5)2TiMe.17,20
∆
2(C5HMe4)2TiMe
8
-2CH4
2
[(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 (1)
4
Molecu la r Str u ctu r e of [(C5HMe4)(µ-η1:η5-C5Me4)-
Ti]2 (4). The molecular structure of 4 is shown in
Figure 1. Selected bond distances and angles are shown
in Table 1 and details of the X-ray structure determi-
nation in Table 3. Compound 4 possesses a crystallo-
graphically imposed Ci symmetry. Each titanium atom
is π-bonded to a C5HMe4 and a C5Me4Ti ligand and
σ-bonded to a neighboring cyclopentadienyl to form a
C5Me4Ti group.21 In fact, the structure of each (C5-
HMe4)(η5-C5Me4)Ti(η1-C5Me4) moiety is very similar to
that of the monomeric (C5Me5)2TiR compounds.17 In (C5-
Me5)2TiCH2CMe3 the Ti-C σ-bond is 2.235(4) Å, which
is comparable to the Ti-C σ-bond of 2.193(2) Å in 4.
The C5HMe4-Ti-C5Me4 angle is 141.43(2)°, which is
only slightly larger than the CE-Ti-CE (CE ) Cp ring
centroid) angle of 139.4(3)° in (C5Me5)2TiCH2CMe3. The
Ti-CE distances of 2.0231(9) and 2.0515(9) Å for the
C5Me4 and the C5HMe4 ligands, respectively, are also
(11) Mach, K.; Raynor, J . B. J . Chem. Soc., Dalton Trans. 1992, 683-
688.
(12) (a) Brintzinger, H. H.; Bercaw, J . E. J . Am. Chem. Soc. 1970,
92, 6182-6185. (b) Davison, A.; Wreford, S. S. J . Am. Chem. Soc. 1974,
96, 3017-3018. (c) Troyanov, S. I.; Antropiusova´, H.; Mach, K. J .
Organomet. Chem. 1992, 427, 48-55.
(13) The X-ray structure of [µ-C16H20][(C5Me3H2)Ti(µ-H)]2 derived
from 1,2,3-trimethylcyclopentadienyl compounds has recently been
determined. Varga, V.; Mach, K.; Pola´sˇek, M.; Sedmera, P.; Hiller,
J .; Thewalt, U.; Troyanov, S. I. J . Organomet. Chem. 1996, 506, 241-
251.
(14) Troyanov, S. I.; Mach, K.; Varga, V. Organometallics 1993, 12,
3387-3389.
(15) 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.
(16) Mach, K.; Varga, V.; Hanusˇ, V.; Sedmera, P. J . Organomet.
Chem. 1991, 415, 87-95.
(20) Luinstra, G. A.; Teuben, J . H. J . Am. Chem. Soc. 1992, 114,
3361-3367.
(21) A very similar structure has been obtained with C5H2Me3
ligands instead of C5HMe4. [(C5H2Me3)(µ-η1:η5-C5HMe3)Ti]2: (C16H21
-
(17) Luinstra, G. A.; Ten Cate, L. C.; Heeres, H. J .; Pattiasina, J .
W.; Meetsma, A.; Teuben, J . H. Organometallics 1991, 10, 3227-3237.
(18) The resonances are integrated according to the expected
intensities.
(19) Luinstra, G. A.; Teuben, J . H. J . Chem. Soc., Chem. Commun.
1990, 1470-1471.
Ti)2, Mr ) 522.44, triclinic, P1h, a ) 8.819(1) Å, b ) 9.026(1) Å, c )
9.899(1) Å, R ) 102.08(1)°, â ) 101.866(9)°, γ ) 113.353(8)°, V ) 669.85-
(14) Å3, Z ) 1, Dexptl ) 1.295 g cm-3, λ(Mo KRj) ) 0.710 73 Å, µ ) 6.1
cm-1, T ) 130 K, RF ) 0.039 for 2830 unique observed reflections with
I g 2.5σ(I) and 238 parameters. Mach, K.; Teuben, J . H.; Meetsma,
A. Unpublished results.

Bis(tetramethylcyclopentadienyl)titanium Chemistry
Organometallics, Vol. 15, No. 23, 1996 4979
in the range normally observed.5 The ring slippage
(0.129 Å, with the shortest Ti-C distance toward the
unsubstituted carbon atom) of the C5HMe4 ligand has
been observed for other (C5HMe4)2Ti complexes.5 The
bridging C5Me4 ligand displays a somewhat larger ring
slippage (0.176 Å, with the shortest Ti-C distance
toward the η1-bonded carbon atom). The Ti-Ti distance
(3.5430(6) Å) is significantly longer than the Ti-Ti
distance in (C5H5)3(µ-η1:η5-C5H4)Ti2(THF) (3.336(4) Å)22
or in [(C5H5)(µ-η1:η5-C5H4)Ti(PMe3)]2 (3.223(1) Å).23 The
η5- and η1-Ti-C bond lengths of these two complexes
are comparable to those in 4. Similar structures with
µ-η1:η5-cyclopentadienyl ligands have been found for
nium(III) hydride, (C5Me5)2TiH.27a,29 Recently the mo-
lecular structure of the first monomeric titanocene(III)
hydride (C5PhMe4)2TiH has been determined.30 These
titanocene(III) hydrides are intriguing compounds, be-
cause of their key role in the “titanocene enigma” and
their activity as catalysts for many organic reactions.30
Upon hydrogenolysis of (C5HMe4)2TiR (R ) Me (2), R
) Ph (3)), the green solution turned red-brown, char-
acteristic for formation of titanocene(III) hydride (C5-
HMe4)2TiH (5). To¨pler pump analysis of the gas formed
on reaction of 2 with D2 revealed that 1 equiv of CH3D/
Ti had been liberated. Surprisingly, as soon as N2 was
admitted to a solution of 5, a blue precipitate formed,
which prevented isolation and characterization of the
pure hydride.31 However, the close similarity between
the NMR (broad resonances for the methyl substituents
of the C5HMe4 ligands are at 46.4 and 9.6 ppm; no
resonances for the hydride proton or the ring protons
are observed) and ESR (singlet at g ) 1.9789, with a(Ti)
) 9.3 G) solution spectra of the red-brown 5 with those
of (C5Me5)2TiH29a and (C5PhMe4)2TiH30 reliably allows
identification as (C5HMe4)2TiH. Additional proof was
obtained from reactivity studies. When 1,3-butadiene
was admitted to a solution of 5, purple (C5HMe4)2Ti(η3-
1-methylallyl) (7) was formed exclusively, indicating
that 5 behaves as a regular titanocene(III) hydride.32
In analogy to (C5Me5)2TiH29a and (C5PhMe4)2TiH,30
oxidation of 5 with PbCl219 yielded the diamagnetic (C5-
HMe4)2Ti(H)Cl (6), in which the hydride resonance
appears at 4.10 ppm in the 1H NMR spectrum. The
hydride 5 is not as stable as the corresponding hydrides
of (C5Me5)2TiH and (C5PhMe4)2TiH, because at room
temperature crystalline 4 slowly separates from solu-
tions of 5, accompanied by liberation of H2.
It is remarkable that 5 immediately reacts with even
traces of N2 at room temperature, whereas (C5Me5)2-
TiH29a and (C5PhMe4)2TiH30 appear to be completely
indifferent toward N2 at room temperature, even under
1 atm of N2. The dramatic color change from red-brown
to blue upon exposure of a solution of 5 to N2 gas,
followed by the separation of shiny metal-luster crystals,
suggests the formation of the dinitrogen complex [(C5-
HMe4)2TiH]2N2, like their regular cyclopentadienyl
analogs (Cp2TiR)2N2.33 However, formation of H2 dur-
ing complexation of N2 indicates a more complicated
reaction sequence. An X-ray structure determination
of the product showed that instead of the dinuclear
titanocene(III) dinitrogen complex [(C5HMe4)2TiH]2N2
the dinitrogen complex of titanocene(II) [(C5HMe4)2-
Ti]2N2 (8) had been formed.
24
other metals, e.g. [(C5H5)2Th(µ-C5H4)]2 and [(C5H5)2-
Nb(H)(µ-C5H4)]2.25
F or m a tion of [(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 (4) vs
(C5Me5)(η1:η5-C5Me4CH2)Ti. Both titanocene(III) meth-
yl compounds (C5HMe4)2TiMe (2) and (C5Me5)2TiMe
decompose upon heating, liberating 1 equiv of CH4 per
Ti. The resulting organometallic products are quite dif-
ferent: the dimeric [(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 (4) for
(C5HMe4)2TiMe (2) vs the monomeric (C5Me5)(η1:η5-C5-
Me4CH2)Ti for (C5Me5)2TiMe. Since arene C-H bonds
(sp2 hybridized) are more reactive than aliphatic C-H
bonds (sp3 hybridized),26 it is not surprising that upon
thermolysis of 2, activation of an sp2-hybridized ring
C-H bond is preferred to activation of an sp3-hybridized
methyl C-H. However, thermolysis of (C5Me5)2TiRn (n
) 1, 2) compounds is known to proceed via complicated
mechanisms such as the formation of a carbene inter-
mediate during the thermolysis of (C5Me5)2TiMe2 to (C5-
Me5)(η1:η5-C5Me4CH2)TiMe.27 Another example is the
thermolysis of (C5Me5)2TiR compounds to (C5Me5)(η1:
η5-C5Me4CH2)Ti, which is catalyzed by (C5Me5)2TiH,
formed during the reaction itself.20 A similar autocata-
lytic mechanism, including the activation of the ring
C-H bond, may well take place in the decomposition of
2 to 4, but the actual thermolysis mechanism was not
studied. An intramolecular activation of the ring C-H
bond would lead to a highly constrained monomeric (C5-
HMe4)(η1:η5-C5Me4)Ti compound, which is considered
unlikely. Though the intermediacy of such a product
cannot be excluded, the formation of stable dimeric 4
presumably occurs via intermolecular activation of ring
C-H bonds, which allows the bridging η1:η5-C5Me4
ligands to retain their planar geometry.28
(C5HMe4)2TiH (5) a n d Rea ction w ith N2. Hydro-
genolysis of (C5Me5)2TiR produces a monomeric tita-
(22) Pez, G. P. J . Am. Chem. Soc. 1976, 98, 8072-8078.
(23) Kool, L. B.; Rausch, M. D.; Alt, H. G.; Herberhold, M.; Thewalt,
U.; Honold, B. J . Organomet. Chem. 1986, 310, 27-34.
(24) Baker, E. C.; Raymond, K. N.; Marks, T. J .; Wachter, W. A. J .
Am. Chem. Soc. 1974, 96, 7586-7588.
Molecu la r Str u ctu r e of [(C5HMe4)2Ti]2N2 (8). The
molecular structure of 8 is shown in Figure 2, and
selected bond distances and angles and details of the
(25) Guggenberger, L. J . Inorg. Chem. 1973, 12, 294-301.
(26) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J .;
Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J . Am.
Chem. Soc. 1987, 109, 203-219.
(27) (a) Bercaw, J . E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H.
H. J . Am. Chem. Soc. 1972, 94, 1219-1238. (b) Bercaw, J . E.;
Brintzinger, H. H. J . Am. Chem. Soc. 1971, 93, 2046-2048. (c)
McDade, C.; Green, J . C.; Bercaw, J . E. Organometallics 1982, 1, 1629-
1634.
(28) The situation is different for the thermolysis of the titanocene-
(IV) dimethyl compound (C5HMe4)2TiMe2,16 which decomposes to the
monomeric fulvene compound (C5HMe4)(C5HMe3CH2)TiMe. Titanium
in (C5HMe4)2TiMe2 is surrounded by four ligands instead of three,
which sterically prevent intermolecular activation of ring C-H bonds.
Instead, intramolecular activation of a less reactive methyl C-H bond
occurs, so that a monomeric fulvene compound is isolated, similar to
the decomposition of (C5Me5)2TiMe2 to (C5Me5)(C5Me4CH2)TiMe.26
(29) (a) Teuben, J . H. In Fundamental and Technological Aspects
of Organo-f-Element Chemistry; Marks, T. J ., Fragala, I. L., Eds.;
Reidel: Dordrecht, The Netherlands, 1985; pp 195-227. (b) Bercaw,
J . E. J . Am. Chem. Soc. 1974, 96, 5087-5094.
(30) De Wolf, J . M.; Meetsma, A.; Teuben, J . H. Organometallics
1995, 14, 5466-5468 and references therein.
(31) Even under Ar, formation of an intensely blue solution was
observed. Apparently traces of N2 are sufficient to set off the
disproportionation of 5 and form the dinitrogen complex [(C5HMe4)2-
Ti]2N2 (8).
(32) (a) Mach, K.; Antropiusova´, H.; Varga, V.; Hanusˇ, V. J .
Organomet. Chem. 1988, 358, 123-133. (b) Gao, Y.; Iijima, S.; Urabe,
H.; Sato, F. Inorg. Chim. Acta 1994, 222, 145-153.
(33) (a) Teuben, J . H.; De Liefde Meijer, H. J . Recl. Trav. Chim.
Pays-Bas 1971, 90, 360-363. (b) Zeinstra, J . D.; Teuben, J . H.;
J ellinek, F. J . Organomet. Chem. 1979, 170, 39-50.

4980 Organometallics, Vol. 15, No. 23, 1996
de Wolf et al.
molecule with the center of inversion in the middle of
the N-N bond. No hydride ligands are present. The
CE(1)-Ti-CE(2) angle of 140.99(3)° and the CE(1)-Ti-
N(1) and CE(2)-Ti-N(1) angles of 108.11(9) and 110.33-
(9)° add up to 359.4°, which illustrates a planar trian-
gular coordination around titanium. The distance
between the nitrogen atoms is 1.170(4) Å, which com-
pares well with the N-N distances in [(C5Me5)2Ti]2N2
(1.160(14) Å)34 and [(C5H5)2Ti(4-CH3C6H4)]2N2 (1.162-
(12) Å).33b The Ti-N distance of 1.987(3) Å is between
those found for [(C5Me5)2Ti]2N2 (2.017(12) Å) and [(C5H5)2-
Ti(4-CH3C6H4)]2N2 (1.962(6) Å). The Ti-N-N-Ti skel-
eton is almost linear (Ti(1)-N(1)-N(2) ) 178.5(3)°), as
in [(C5Me5)2Ti]2N2 (177.4(4)°) and [(C5H5)2Ti(4-CH3-
C6H4)]2N2 (176.5(5)°). Within each (C5HMe4)2Ti unit a
staggered conformation is adopted with the sp2 C-H
bond of one C5HMe4 ligand pointing between two methyl
groups of the other. Other dinuclear (C5HMe4)2Ti
complexes display the same orientation of the C5HMe4
ligands.35 In mononuclear (C5HMe4)2Ti complexes such
F igu r e 2. ORTEP drawing (50% probability level) and
atom-labeling scheme for [(C5HMe4)2Ti]2N2 (8). Hydrogen
atoms are omitted for clarity.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d Bon d
An gles (d eg) for [(C5
HMe4)2Ti]2N2 (8)
Ti1-N1
1.987(3)
2.0338(6)
2.327(3)
2.355(3)
2.388(3)
2.394(3)
2.356(4)
N1-N1a
Ti1-CE2a
Ti1-C10
Ti1-C11
Ti1-C12
Ti1-C13
Ti1-C14
1.170(4)
5
Ti1-CE1a
Ti1-C1
Ti1-C2
Ti1-C3
Ti1-C4
Ti1-C5
2.0348(7)
2.312(4)
2.360(3)
2.397(3)
2.399(3)
2.342(4)
as (C5HMe4)2TiCl and (C5HMe4)2TiCl2 the ligands are
staggered too, but with the sp2 C-H bonds of each C5-
HMe4 ligand pointing toward each other, thereby mini-
mizing the steric hindrance between the ligands. In
dinuclear (C5HMe4)2Ti complexes such as 8, such an
orientation would produce more steric hindrance be-
tween the methyl substituents of the two different (C5-
HMe4)2Ti moieties on each side of the bridging N2
ligand.
Ti1-N1-N1a
N1-Ti1-CE1
178.5(3)
108.11(9)
CE1-Ti1-CE2
N1-Ti1-CE2
140.99(3)
110.33(9)
a
CE1 ) C1-C5 ring centroid; CE2 ) C10-C14 ring centroid.
Red u ction of (C5HMe4)2TiH (5) to [(C5HMe4)2-
Ti]2N2 (8). Surprisingly, the Ti(III) hydride 5 is reduced
to the dinuclear Ti(II) N2 complex [(C5HMe4)2Ti]2N2 (8)
upon reaction with N2, under liberation of H2 (eq 2).
Ta ble 3. Deta ils of th e X-r a y Str u ctu r e
Deter m in a tion s of [(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 (4)
a n d [(C5HMe4)2Ti]2N2 (8)
C36H50Ti2 (4)
C36H52N2Ti2 (8)
mol wt
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å
578.55
608.58
N2
triclinic
P1h (No. 2)
8.583(1)
9.249(1)
11.085(1)
68.766(6)
88.553(6)
69.285(4)
761.9(2)
1
monoclinic
P21/c (No. 14)
8.4661(9)
10.3254(12)
20.3205(17)
2(C5HMe4)2TiH
8 [(C5HMe4)2Ti]2N2
(2)
-H2
5
8
The question arises how titanium is reduced from the
3+ to the 2+ oxidation state. Most likely, equilibria are
involved in which the Ti(III) hydride 5 disproportionates
to the Ti(IV) dihydride (C5HMe4)2TiH2 (9) and a Ti(II)
compound, (C5HMe4)2Ti (10) (eq 3). The dihydride 9 can
lose dihydrogen in a subsequent equilibrium reaction
to form the titanocene 10 (eq 4). Such equilibria have
been proposed by Bercaw to explain the decomposition
of (C5Me5)2TiH2.29b
114.541(8)
1615.9(3)
2
1.251
652
Z
D
calcd, g cm-3
1.261
310
5.4
F(000), e
µ(Mo KRj), cm-1
cryst size, mm
radiation, Å
monochromator
temp, K
5.1
0.25 × 0.37 × 0.50 0.25 × 0.25 × 0.25
Mo KRj, 0.710 73
graphite
130
Mo KRj, 0.710 73
graphite
150
6191
3712
2(C5HMe4)2TiH h (C5HMe4)2TiH2 + (C5HMe4)2Ti
total no. of data
no. of unique data 3678
3920
5
9
10
(3)
no. of obsd data
(I g 2.5σ(I))
no. of refined
params
3397
273
2296
(C5HMe4)2TiH2 y-H z (C5HMe4)2Ti
(4)
2
214
9
10
a
RF
0.029
0.039
1
0.625
-0.33, 0.35
0.053
0.054
b
Rw
Next, the titanocene 10 reacts with N2 to form the
dinuclear N2 complex [(C5HMe4)2Ti]2N2 (8) (eq 5).
Because of the consumption of 10 by reaction with N2,
the equilibria 3 and 4 are shifted to the right and
eventually all Ti(III) hydride 5 is converted into 8.
The reactivity of (C5HMe4)2TiH (5) is in contrast with
the related Ti(III) hydrides (C5Me5)2TiH and (C5PhMe4)2-
w
1/[σ2(F) + 0.000413F2]
1.32
Sc
residual
-0.51, 0.48
density, e Å-3
a
b
2
RF ) ∑(||Fo| - |Fc||)/∑|Fo|. Rw ) [∑(w(|Fo| - |Fc|)2)/∑w|Fo| ]1/2
.
c S ) [∑w(|Fo| - |Fc|)2/(m - n)]1/2; m ) number of observations, n
) number of variables.
X-ray structure determination are shown in Tables 2
and 3. Compound 8 is a dinuclear complex, in which
two (C5HMe4)2Ti moieties are bridged by N2 in an
essentially linear arrangement. It is a centrosymmetric
(34) Sanner, R. D.; Duggan, D. M.; McKenzie, T. C.; Marsh, R. E.;
Bercaw, J . E. J . Am. Chem. Soc. 1976, 98, 8358-8365.
(35) (a) Gyepes, R.; Mach, K.; C´ısarova´, I.; Loub, J .; Hiller, J .;
Sˇindela´r, P. J . Organomet. Chem. 1995, 497, 33-41. (b) Troyanov, S.
I.; Varga, V.; Mach, K. J . Organomet. Chem. 1993, 461, 85-90.

Bis(tetramethylcyclopentadienyl)titanium Chemistry
Organometallics, Vol. 15, No. 23, 1996 4981
ylcyclopentadiene36 and TiCl3‚3THF37 were prepared according
to published procedures. The synthesis of (C5HMe4)MgCl was
derived from that of (C5Me5)MgCl.8 H2 (99.995%, Hoek-Loos)
was used without further purification.
N2
9
2(C5HMe4)2Ti
8 [(C5HMe4)2Ti]2N2
(5)
10
8
Syn th esis of (C5HMe4)2TiCl2.38 A mixture of TiCl3‚3THF
(15.9 g, 42.8 mmol) and (C5HMe4)MgCl (21.7 g, 86.0 mmol) in
300 mL of THF was stirred at room temperature for 46 h. A
dark brown solution formed, from which the solvent was
removed by evaporation. The residue was continuously ex-
tracted with pentane. The purple-brown extract was concen-
trated to saturation and cooled to -30 °C. Dark purple needles
of crude 1 separated, which were isolated after washing with
TiH, which are stable under N2 at room temperature.
Unlike the formation of thermolysis product 4, the
difference in reactivity between 5 on one side and (C5-
Me5)2TiH and (C5PhMe4)2TiH on the other cannot be
explained by the availability of sp2 C-H bonds of the
C5HMe4 ligands, as it is unlikely that they are involved
in the reduction of 5 to 8. Since [(C5Me5)2Ti]2N2,34 which
is the pentamethylcyclopentadienyl analog of 8, exists
as well, the slightly reduced steric bulk of C5HMe4
ligands with respect to C5Me5 ligands is unlikely to be
responsible either. The reason for the different reactiv-
ity seems to be electronic. The electron-donating capac-
ity of tetramethylcyclopentadienyl ligands to the tita-
nium(III) center is less than that of pentamethyl-
cyclopentadienyl ligands, which probably causes 5 to be
more susceptible to reduction than (C5Me5)2TiH and (C5-
PhMe4)2TiH.
When a toluene suspension of 8 was stirred under a
dynamic vacuum to remove N2, the blue color disap-
peared and a brown solution resulted, from which a
brown waxy residue was obtained. Admission of N2 to
the brown solution restored 8 quantitatively. The
brown product showed no reaction with 1,3-butadiene;
therefore, it cannot be hydride 5.32a In analogy with
the formation of (C5Me5)2Ti upon degassing [(C5Me5)2-
Ti]2N2,29b this compound was tentatively identified as
titanocene (C5HMe4)2Ti (10). Admission of H2 to solu-
tions of 10 resulted in formation of hydride 5. Presum-
ably the titanocene 10 reacts with H2 to give the
titanocene(IV) dihydride (C5HMe4)2TiH2 (9). Com-
pounds 9 and 10 then subsequently conproportionate
to the monohydride 5 (eq 3).
19
pentane. Oxidation of crude 1 with excess PbCl2 in THF
yielded a red solution, which was filtered, saturated, and cooled
to -80 °C. Pure (C5HMe4)2TiCl2 was isolated as red-brown
needles. Yield: 9.25 g, 60% relative to TiCl3‚3THF. 1H NMR
(200 MHz, C6D6): δ 5.37 (s, 2H, C5HMe4), 2.06, 1.65 (s, 12H,
C5HMe2Me2).
Syn th esis of (C5HMe4)2TiCl (1).5 Compound 1 was made
by reduction39 of (C5HMe4)2TiCl2. To a suspension of (C5-
HMe4)2TiCl2 (1.51 g, 4.18 mmol) in 30 mL of diethyl ether were
added 0.4 mL of 1,4-dioxane (4.7 mmol) and 3.4 mL of a
solution of iPrMgCl in diethyl ether (1.23 M, 4.2 mmol). After
this mixture was stirred for 2 h, a blue solution had formed.
The volatiles were removed by evaporation, and the residue
was extracted with pentane. Concentration and cooling to -80
°C afforded 1.23 g (90%) of 1 as dark blue needles. 1H NMR
(200 MHz, C6D6): δ 43 (s, 12 H, C5HMe2Me2, WHM (peak width
at half maximum height) ) 2.75 kHz), 0.3 (s, 12H, C5HMe2Me2,
WHM ) 160 Hz). IR (KBr/Nujol, cm-1): 3086 (w), 2724 (w),
1500 (w), 1024 (s), 858 (s), 440 (s).
Syn th esis of (C5HMe4)2TiMe (2). To 1.24 g of 1 (3.81
mmol) dissolved in 30 mL of diethyl ether was added 2.3 mL
of a solution of MeLi in diethyl ether (1.64 M, 3.8 mmol). After
it was stirred for 1 h, the reaction mixture had turned dark
green. It was evaporated to dryness, and the residue was
extracted with pentane. Evaporation of solvent gave 0.92 g
of 2 (79%) as a green powder. 1H NMR (200 MHz, toluene-
d8): δ 48 (s, 12 H, C5HMe2Me2, WHM ) 3.50 kHz), 3.0 (s, 12
H, C5HMe2Me2, WHM ) 115 Hz), -26 (s, 3 H, TiMe, WHM )
1.19 kHz). IR (KBr/Nujol, cm-1): 3081 (w), 2724 (w), 1501
(w), 1024 (s), 835 (s), 692 (s), 606 (s), 432 (m). UV/vis (toluene,
Con clu sion s
nm): 313, 350 (sh), 450, 585. ESR (toluene, 23 °C): giso
)
Comparison of bis(cyclopentadienyl)titanium(III) com-
pounds (C5HMe4)2TiR and their permethylcyclopenta-
dienyl analogs (C5Me5)2TiR shows that replacement of
one methyl group of the pentamethylcyclopentadienyl
ligands by hydrogen has a dramatic effect on the
reactivity, as follows from a study of the thermolysis of
(C5HMe4)2TiR compounds and the reactivity of the
hydride toward N2. The formation of the dimeric
thermolysis product [(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 (4)
can be explained by the presence of one sp2 C-H bond
in the tetramethylcyclopentadienyl ligand, which opens
up another metalation pattern than in the correspond-
ing pentamethylcyclopentadienyl compounds, in which
only sp3 C-H bonds are available. The difference in
the reactivity toward N2 of hydride (C5HMe4)2TiH (5),
yielding [(C5HMe4)2Ti]2N2 (8), on one side and homolo-
gous hydrides (C5Me5)2TiH and (C5PhMe4)2TiH on the
other, is ascribed to a subtle variation of electronic
properties induced by these ligands, resulting in a
slightly higher Lewis acidity of the metal center in
hydride 5.
1.9637, ∆H ) 14 G. ESR (toluene, -130 °C): g1 ) 1.9983, g2
) 1.9831, g3 ) 1.9137, gav ) 1.9650. ESR (MTHF, 23 °C): giso
) 1.9633, ∆H ) 17 G. ESR (MTHF, -150 °C): g1 ) 1.9982,
g2 ) 1.9822, g3 ) 1.9153, gav ) 1.9652. Oxidation of 2 with
PbCl219 in diethyl ether quantitatively yielded red (C5HMe4)2-
Ti(Me)Cl. 1H NMR (200 MHz, C6D6): δ 4.79 (s, 2H, C5HMe4),
2.11, 1.99, 1.74, 1.42 (s, 6H, C5HMe4), 0.21 (s, 3H, TiMe).
Syn th esis of (C5HMe4)2TiP h (3). A 1.26 g amount of (C5-
HMe4)2TiCl2 (3.50 mmol) was reduced to 1 (vide supra). To
the diethyl ether suspension of 1 was added 3.8 mL of a diethyl
ether solution of PhMgBr (1.0 M, 3.8 mmol), after which the
reaction mixture was stirred for 1 h. A dark green solution
had formed. The solvent was removed by evaporation, and
the residue was extracted with pentane. Concentration and
cooling to -80 °C gave two crops of dark green crystals.
Yield: 1.21 g of 3 (94%). 1H NMR (200 MHz, toluene-d8): δ
40 (s, 12H, C5HMe2Me2, WHM ) 5.2 kHz), 23 (s, 2 H, Hortho
,
WHM ) 1.8 kHz), 13.6 (s, 1 H, Hpara, WHM ) 240 Hz), 4.1 (s,
12 H, C5HMe2Me2, WHM ) 200 Hz), -1.0 (m, 2H, Hmeta, WHM
) 230 Hz). IR (KBr/Nujol, cm-1): 3042 (w), 2726 (w), 2361
(36) (a) Fendrick, C. M.; Schertz, L. D.; Day, V. W.; Marks, T. J .
Organometallics 1988, 7, 1828-1838. (b) Szymoniak, J .; Besanc¸on,
J .; Dormond, A.; Mo¨ıse, C. J . Org. Chem. 1990, 55, 1429-1432.
(37) Manzer, L. E.; Deaton, J .; Sharp, P.; Schrock, R. R. Inorg. Synth.
1982, 21, 137.
Exp er im en ta l Section
(38) Mach, K.; Varga, V.; Antropiusova´, H.; Pola´cek, J . J . Organomet.
Chem. 1987, 333, 205-215.
(39) (a) Direct synthesis of 1 via reaction of TiCl3‚3THF with (C5-
HMe4)MgCl led to contamination of 1 with (C5HMe4)2TiCl2. (b) Martin,
H. A.; J ellinek, F. J . Organomet. Chem. 1967, 8, 115-128.
Gen er a l Com m en ts. All manipulations of air-sensitive
compounds were carried out under N2, using standard Schlenk-
line and glovebox or vacuum-line techniques. All solvents were
distilled from Na/K alloy or LiAlH4 prior to use. Tetrameth-

4982 Organometallics, Vol. 15, No. 23, 1996
de Wolf et al.
(w), 1562 (w), 1412 (w), 1233 (w), 1173 (w), 1150 (w), 1113
(w), 1049 (w), 1022 (s), 824 (vs), 721 (vs), 704 (vs), 610 (m),
473 (s), 428 (s). Oxidation with PbCl219 quantitatively yielded
red (C5HMe4)2Ti(Ph)Cl. 1H NMR (200 MHz, toluene-d8): δ
7.36 (d, 1H, Hortho, J ) 6.4 Hz), 7.01 (m, 2H, Hmeta), 6.90 (m,
1H, Hpara), 6.20 (d, 1H, Hortho), 4.95 (s, 2H, C5HMe4), 1.94, 1.75,
1.62, 1.52 (s, 6H, C5HMe4).
Syn th esis of [(C5HMe4)(µ-η1:η5-C5Me4)Ti]2 (4) by Th er -
m olysis of (C5HMe4)2TiMe (2). A solution of 2 (1.23 g, 4.03
mmol) in 20 mL of toluene in a sealed ampule was heated to
130 °C for 4 h. The green-brown solution was cooled to room
temperature slowly, and dark green-brown crystals separated,
which were isolated and washed with pentane. Yield: 0.78 g
of 4 (67%). MS (75 eV, m/e): 578 (M+). UV/vis (toluene, nm):
295, 360 (sh), 435, 525, 610 (sh). Anal. Calcd for C36H50Ti2:
C, 74.74; H, 8.71; Ti, 16.55. Found: C, 74.65; H, 8.67; Ti,
16.63. In an identical manner 4 was synthesized by thermoly-
sis of 3; GC analysis showed the formation of benzene during
the thermolysis. The thermolysis product 4 was also synthe-
sized by removing H2 (MS analysis) from a solution of hydride
5 in hexane under a dynamic vacuum.
factors taken from Cromer and Liberman47 were included in
Fc. All calculations were carried out on the CDC-Cyber 962-
31 computer of the University of Groningen with the program
packages XTAL,48 EUCLID49 (calculation of geometric data),
and ORTEP50 (preparation of illustrations).
Syn th esis of (C5HMe4)2TiH (5). A 0.83 g portion of (C5-
HMe4)2TiPh (3; 2.26 mmol) was dissolved in pentane and
degassed thoroughly by several freeze/pump/thaw cycles. H2
was admitted to the frozen solution, which was warmed to
room temperature with stirring. The color of the solution
changed to red-brown. It proved impossible to isolate pure 5
from this solution, since it reacted immediately with the
slightest trace of N2 and small crystals of 4 separated as well.
1H NMR (200 MHz, C6D6): δ 46.4 (s, 12 H, C5HMe2Me2, WHM
) 1.68 kHz), 9.6 (s, 12 H, C5HMe2Me2, WHM ) 160 Hz). ESR
(toluene): g ) 1.9789, ∆H ) 5 G, a(Ti) ) 9.3 G. In an identical
manner 5 was synthesized by hydrogenolysis of 2.
19
Syn th esis of (C5HMe4)2Ti(H)Cl (6). Excess PbCl2 was
added to a C6D6 solution of 30 mg of 5. After filtration a red-
brown solution of (C5HMe4)2Ti(H)Cl (6) was obtained. 1H NMR
(200 MHz, C6D6): δ 4.68 (s, 2H, C5HMe4), 4.10 (s, 1H, TiH),
2.19, 2.09, 1.77, 1.74 (s, 6H, C5HMe4).
Th er m olysis of (C5HMe4)2TiMe (2): Ga s An a lysis. On
a vacuum line a solution of 0.069 g of 2 (0.226 mmol) in 5 mL
of toluene was heated to 130 °C for 4 h. The amount of
liberated gas was measured using a To¨pler pump: 0.224 mmol
(0.99 mol/mol of Ti). It was analyzed as methane (MS).
Rea ction of (C5HMe4)2TiMe (2) w ith D2: Ga s An a lysis.
A solution of 0.114 g of 2 (0.374 mmol) in pentane was
degassed by three freeze/pump/thaw cycles. A 0.692 mmol
amount of D2 was admitted to the solution, yielding a red-
brown solution. The amount of liberated gas and excess of D2
were measured using a To¨pler pump (0.710 mmol). The gas
mixture was cycled over a CuO column at 300 °C in order to
burn D2. D2O was collected in a trap cooled with liquid
nitrogen, leaving 0.391 mmol of gas (1.05 mol/mol of Ti), which
was analyzed as CH3D (MS).
Rea ction of (C5HMe4)2TiH (5) w ith 1,3-Bu ta d ien e:
Syn t h esis of (C5HMe4)2Ti(η3-1-m et h yla llyl) (7). To a
stirred solution of 0.87 g of 5 (3.0 mmol) in 20 mL of hexane
was admitted 1,3-butadiene. The red-brown solution turned
intensely purple immediately. After evaporation of the solvent
a purple solid was isolated, which was characterized spectro-
scopically as (C5HMe4)2Ti(η3-1-methylallyl) (7).32a Yield: 0.96
g (93%).
Syn th esis of [(C5HMe4)2Ti]2N2 (8). To a degassed solution
of 1.00 g of 2 (3.28 mmol) in 20 mL of pentane was admitted
H2. The solution was stirred for 2 h, during which time the
H2 atmosphere was refreshed several times. A red-brown
solution of 5 had formed, which was cooled to 0 °C. N2 was
allowed to slowly diffuse into the solution. Beautiful shiny
metal-luster crystals formed, which were isolated from the
dark blue solution by filtration and washed with pentane.
Yield: 0.73 g of 8 (73%). UV/vis (toluene, nm): 310 (sh), 350
(sh), 592. Anal. Calcd for C36H52N2Ti2: C, 71.04; H, 8.61; N,
4.60; Ti, 15.74. Found: C, 70.94; H, 8.65; N, 4.43; Ti, 15.62.
X-r a y Str u ctu r e Deter m in a tion of [(C5HMe4)2Ti]2N2 (8).
Suitable single crystals of 8 were grown by slow diffusion of
X-r a y Str u ctu r e Deter m in a tion of [(C5HMe4)(µ-η1:η5-
C5Me4)Ti]2 (4). Single crystals of 4 were grown by slow
cooling of a hot toluene solution of 4. A green-brown paral-
lelepiped crystal was selected, glued on a glass fiber in a
drybox, transferred to the goniostat, and cooled to 130 K using
an on-line liquid nitrogen cooling system mounted on an Enraf-
Nonius CAD-4F diffractometer interfaced to a VAX-11/730
computer. Unit cell parameters were determined from a least-
squares treatment of the setting angles of 22 reflections in the
range 13.18° < θ < 18.88° in four alternate settings.40
A
search of a limited hemisphere of reciprocal space yielded a
set of reflections that showed no evidence of symmetry or
systematic extinction. The unit cell was identified as triclinic,
space group P1h. This choice was confirmed by the solution
and the successful refinement in this space group of the
structure. Reduced cell calculations did not indicate any
higher metrical lattice symmetry,41 and examination of the
final atomic coordinates of the structure did not yield extra
metric symmetry elements.42 The structure was solved by
Patterson methods and subsequent partial structure expansion
(SHELXS8643). The positional and anisotropic thermal pa-
rameters for the non-hydrogen atoms were refined with block-
diagonal least-squares procedures (XTAL44), minimizing the
function Q ) ∑h[w|Fo| - |Fc|)2]. A subsequent difference
Fourier synthesis gave all the hydrogen atoms, whose coordi-
nates and isotropic thermal parameters were refined. Final
full-matrix least-squares refinement (based on Fo) with aniso-
tropic thermal parameters for the non-hydrogen atoms and
isotropic thermal parameters for the hydrogen atoms con-
verged at RF ) 0.029 (Rw ) 0.039, w ) 1). The crystal
exhibited some secondary extinction, for which the F values
were corrected by refinement of an empirical isotropic extinc-
tion parameter.45 A final difference Fourier map did not show
residual peaks outside the range (0.35 e/Å3. Scattering factors
were taken from Cromer and Mann.46 Anomalous dispersion
N2 into a pentane solution of 5. A crystal sealed in
a
Lindemann-glass capillary was mounted on an Enraf-Nonius
CAD4-T diffractometer on a rotating anode and was held under
a cold nitrogen stream. Accurate unit-cell parameters and an
orientation matrix were determined from the setting angles
of 25 well-centered reflections (SET4)40 in the range 10.0° < θ
< 14.0°. The unit-cell parameters were checked for the
presence of higher lattice symmetry.41 Data were corrected
for Lp effects. Standard deviations of the intensities as
obtained by counting statistics were increased according to an
analysis of the excess variance of the reference reflections: σ2-
(40) De Boer, J . L.; Duisenberg, A. J . M. Acta Crystallogr. 1984,
A40, C410.
(41) Spek, A. L. J . Appl. Crystallogr. 1988, 21, 578-579.
(42) Le Page, Y. J . Appl. Crystallogr. 1987, 20, 264-269.
(43) Sheldrick G. M. SHELXS86, Program for Crystal Structure
Solution; University of Go¨ttingen, Go¨ttingen, Germany, 1986.
(44) Olthof-Hazekamp, R. In “CRYLSQ”, XTAL2.6 User’s Manual;
Hall, S. R., Stewart, J . M., Eds.; Universities of Western Australia
and Maryland, 1989.
(45) Zachariasen, W. H. Acta Crystallogr. 1967, 23, 558-564.
(46) Cromer, D. T.; Mann, J . B. Acta Crystallogr. 1968, A24, 321-
324.
(47) Cromer, D. T.; Liberman, D. J . Chem. Phys. 1970, 53, 1891-
1898.
(48) Hall, S. R.; Stewart, J . M. XTAL2.6 User’s Manual; Universities
of Western Australia and Maryland, 1989.
(49) Spek, A. L. The EUCLID Package. In Computational Crystal-
lography; Sayre, D., Ed.; Oxford University Press (Clarendon): London,
New York, 1982; p 528.
(50) J ohnson, C. K. ORTEP; Report ORNL-3794; Oak Ridge Na-
tional Laboratory, Oak Ridge, TN, 1965.

Bis(tetramethylcyclopentadienyl)titanium Chemistry
Organometallics, Vol. 15, No. 23, 1996 4983
(I) ) σcs(I) + (pI)2, with p ) 0.01.51 An empirical absorption/
extinction correction was applied (DIFABS52). The structure
was solved by automated Patterson methods and subsequent
difference Fourier techniques (DIRDIF-92).53 Refinement on
F was carried out by full-matrix least-squares techniques
(SHELX7654). Hydrogen atoms (except the Cp-ring hydrogens)
were included in the refinement on calculated positions (C-H
) 0.98 Å), riding on their carrier atoms. Weights were
optimized in the final refinement cycles. The final difference
map was inspected for possible hydride atoms. The largest
peaks are within 1.5 Å from Ti but were rejected, being
artifacts. Neutral atom scattering factors were taken from
Cromer and Mann46 and anomalous dispersion corrections
from Cromer and Liberman.47 Geometrical calculations and
the ORTEP illustrations were done with PLATON.49
Ack n ow led gm en t. This work was supported in part
(N.V. and A.L.S.) by the Netherlands Foundation of
Chemical Research (SON) with financial aid from the
Netherlands Foundation for Scientific Research (NWO).
(51) McCandlish, L. E.; Stout, G. H.; Andrews, L. C. Acta Crystallogr.
1975, A31, 245-249.
Su p p or tin g In for m a tion Ava ila ble: Further details of
the structure determinations, including tables of atomic
coordinates, bond lengths and angles, and thermal parameters
for 4 and 8 (20 pages). Ordering information is given on any
current masthead page.
(52) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158-166.
(53) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garc´ıa-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF Program System, Technical Report of the Crystallography
Laboratory; University of Nijmegen, Nijmegen, The Netherlands, 1992.
(54) Sheldrick, G. M. SHELX76, Program for Crystal Structure
Determination; University of Cambridge, Cambridge, U.K., 1976.
OM960509W