Synthesis, reactivity, and computational studies of [η5- C5H5-(η5-C5H4CMe 2C6H4Me)TiMe]+: Aromatic C-H bond activation at -50 °C

Article abstract of DOI:10.1021/om8000394

The titanocene compound [η⁵-C₅H ₅-(η⁵-C₅H₄CMe₂C ₆H₄Me)TiMe₂] (1) was prepared from the titanocene dichloride precursor [η⁵-C₅H ₅-(η⁵-C₅H₄CMe₂C ₆H₄Me)TiCl₂] (1a). The solid-state structures of 1a and 1 were determined and are similar to other titanocene compounds. The reaction of compound 1 with B(C₆F₅)₃ in CD ₂Cl₂ was monitored by NMR spectroscopy. At -60 °C the expected cationic compound [η⁵-C₅H₅(η ⁵: η¹-C₅H₄CMe₂C ₆H₄Me)TiMe]⁺ (2) with a coordinated tolyl group was observed. Warming the samples to -50 °C leads to evolution of methane, indicating C-H bond activation of the coordinated tolyl moiety. The so-formed titanacycles form with the anion [MeB(C₅F₅) ₃]^- the inner sphere ion pair (ISIP) [η ⁵C₅H₅-(η⁵:σ¹ -C₅H₄CMe₂C₆H₃Me)Ti-μ- MeB(C₆F₅)₃] (3) and is in exchange with an outer sphere ion pair η⁵-C₅H₅- (η⁵:σ¹-C₅H₄CMe ₂C₆H₃Me)Ti]⁺[MeB(C₆F ₅)₃]- (4), with the free coordination site probably occupied by a solvent molecule. The structure of 4 could not be determined unambiguously. The homoleptic bimetallic compound [{η⁵-C ₅H₅-(η⁵-C₅H₄CMe ₂C₆H₄Me)Ti}₂-μ-Me]⁺ (5) was prepared by reaction of 2 equiv of 1 with 1 equiv of B(C ₆F₅)₃ in CD₂Cl₂ at -50 °C and monitored by NMR spectroscopy. Detailed density functional theory (DFT) studies of the formation of 3 and 4 from 2 corroborate the NMR results.

Full text of DOI:10.1021/om8000394

1996
Organometallics 2008, 27, 1996–2003
Synthesis, Reactivity, and Computational Studies of
[η5-C5H5-(η5-C5H4CMe2C6H4Me)TiMe]+: Aromatic C-H Bond
Activation at -50 °C§
Jörg Sassmannshausen*,† and Judith Baumgartner‡
Institute for Chemistry and Technology of Organic Materials, TU-Graz, Stremayrgasse 16/I A-8010 Graz,
Austria, and Inorganic Chemistry, TU-Graz, Stremayrgasse 16/I A-8010 Graz, Austria
ReceiVed January 15, 2008
The titanocene compound [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiMe2] (1) was prepared from the titanocene
dichloride precursor [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiCl2] (1a). The solid-state structures of 1a and 1
were determined and are similar to other titanocene compounds. The reaction of compound 1 with B(C6F5)3
in CD2Cl2 was monitored by NMR spectroscopy. At -60 °C the expected cationic compound [η5-C5H5(η5:
η1-C5H4CMe2C6H4Me)TiMe]+ (2) with a coordinated tolyl group was observed. Warming the samples
to -50 °C leads to evolution of methane, indicating C-H bond activation of the coordinated tolyl moiety.
The so-formed titanacycles form with the anion [MeB(C6F5)3]- the inner sphere ion pair (ISIP) [η5-
C5H5-(η5:σ1-C5H4CMe2C6H3Me)Ti-µ-MeB(C6F5)3] (3) and is in exchange with an outer sphere ion pair
η5-C5H5-(η5:σ1-C5H4CMe2C6H3Me)Ti]+[MeB(C6F5)3]- (4), with the free coordination site probably
occupied by a solvent molecule. The structure of 4 could not be determined unambiguously. The homoleptic
bimetallic compound [{η5-C5H5-(η5-C5H4CMe2C6H4Me)Ti}2-µ-Me]+ (5) was prepared by reaction of 2
equiv of 1 with 1 equiv of B(C6F5)3 in CD2Cl2 at -50 °C and monitored by NMR spectroscopy. Detailed
density functional theory (DFT) studies of the formation of 3 and 4 from 2 corroborate the NMR results.
hextuples.15 Whereas the chemistry of zirconocene compounds
Introduction
appears to be quite predictable, the chemistry of the titanocene
compounds is sometimes quite unexpected. For example, some
Group 4 metallocene compounds play an important role as
catalyst precursors for the hydrogenation,1 hydrosilylation, and
polymerization of olefins.2–14 In particular for alkene polym-
erization, these precursors need to be activated by a cation-
generating compound (CGA) to form what is believed to be
the active species [η-Cp2MR]+ (Cp ) (substituted) cyclopen-
tadienyl, M ) Ti, Zr, Hf). Obviously, this rather “naked” ion
does not exist by itself in solution; rather it is paired with a
weakly coordinating ligand [Cp2MR+ · · · D] (D ) X- (anion),
monomer, solvent). Depending on the concentration, these anion/
cation pairs form higher conglomerates like quadruples and
time ago we have reported the formation of quasi liVing
polymerization of propene at ambient temperature with the
catalytical mixture of [η5-C5Me5TiMe3] with B(C6F5)3.16,17
Hessen reported the selective trimerization of ethene with half-
sandwich compounds of titanium with coordinated arene
groups.18–20 We have recently reported the formation of cationic
zirconocene compounds with coordinated arene groups and
found that the strength of the coordination strongly depends on
the bridging atom of the tether: Whereas a carbon bridge
between cyclopentadienyl and arene moieties exclusively gave
coordination of the arene to the cationic zirconium, silicon as a
bridging atom resulted in a more ambivalent behavior. Here,
two different products could be observed: the expected zir-
conocene cation with a coordinated arene group and the well-
known inner sphere ion pair with a zirconium-methyl-boron
bridge and a free arene.21–26 We reasoned that the coordination
* Corresponding author. E-mail: sassmannshausen@tugraz.at.
§ Dedicated to F. Stelzer on the occasion of his 60th birthday.
† Institute for Chemistry and Technology of Organic Materials.
‡ Inorganic Chemistry.
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10100–10101.
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Ed. 1999, 38, 428–447.
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10.1021/om8000394 CCC: $40.75
2008 American Chemical Society
Publication on Web 04/10/2008

Synthesis of [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiMe]+
Organometallics, Vol. 27, No. 9, 2008 1997
Scheme 1. (i) LiC6H4Me; (ii) CpTiCl3; (iii) MeLi
of the arene is strongly susceptible to the steric environment of
the metal and thus replaced the metal center with the smaller
titanium. We here extend our recent studies on these model
systems and report the outcome of detailed NMR and DFT
investigations of monosubstituted titanocene compounds of the
general type [η5-Cp-(η5-C5H4CMe2C6H4Me)TiMe]+ (Cp )
C5H5). This combination of NMR and DFT investigations has
proven to be very successful in the past21 and enables investiga-
tion of otherwise unobservable reactive intermediates. In Part
I, the reaction of 1 with B(C6F5)3 in CD2Cl2, investigated by
NMR spectroscopy, is discussed. Part II reports the DFT
investigation of 2 and the formation of 3 and 4, respectively.
suggested structure and agree well with previous results for
the zirconocene congener. As expected, the chemical shift of
the methyl borate anion δ (ppm) at 0.41 (1H) and a broad peak
at 10 ppm (13C) together with the chemical shift difference
∆δ(m,p) of the aryl fluorines of 2.7 ppm are indicative for an
Results and Discussion
Part I: Preparation of the Metallocenes (1a, 1) and
Low-Temperature NMR Investigations. The compounds 1a
and 1 were synthesized according to a modified literature
procedure.22 Thus, LiC6H4Me, freshly prepared from 4-bromo-
toluene and butyllithium, was reacted with 2,2-dimethylfulvene.
The reaction was quenched by addition of [η5-CpTiCl3].
Recrystallization from toluene yielded crystals of 1a suitable
for X-ray analysis in 62.5% yield. Methylation of 1a with
methyllithium in toluene yielded 1. Crystals suitable for X-ray
analysis were obtained after recrystallization from pentane in
good yield (Scheme 1).
Figure 1. ORTEP representation of 1a. Ellipsoids are drawn with
50% probability. Hydrogens are omitted for clarity.
The solid-state structures of 1a and 1 are depicted in Figures
1 and 2, respectively. Typically for this kind of compound, the
arene moiety is pointing away from the titanium in a similar
arrangement to the previously published solid-state structure of
[η5-Cp-η5-(C5H4CMe2C6H4Me)ZrMe2].22 Selected bond dis-
tances and angles are summarized in Table 1.
Low-Temperature NMR Spectroscopy Reaction Studies.
The reaction of 1 with B(C6F5)3 in CD2Cl2 was monitored by
NMR spectroscopy. Similar to the reported compound [η5-Cp-
(η5-C5H4CMe2C6H4Me)ZrMe2], which reacted cleanly at -60
°C to form the outer sphere ion pair (OSIP) [η5-Cp-(η5-
C5H4CMe2C6H4Me)ZrMe]+[MeB(C6F5)3]- as the sole prod-
uct,22 the observed reaction between 1 and B(C6F5)3 yields the
OSIP [η5-C5H5-(η5:η1-C5H4CMe2C6H4Me)TiMe]+[MeB(C6-
F5)3]- (2). Significant are the peaks for the coordinated tolyl
moiety, which are observed as doublets at δ (ppm) 7.74, 7.44,
6.77, and 5.78. EXSY (exchange spectroscopy) at this temper-
ature reveals exchange between the ortho and meta hydrogens,
indicating a fluxional coordination of the tolyl moiety to the
cationic titanium metal. The four observed signals for the
substituted cyclopentadienyl ring together with the two diaste-
reotopic signals for the -C(CH3)2 further corroborate the
Figure 2. ORTEP representation of 1. Ellipsoids are drawn with
30% probability. Hydrogens are omitted for clarity.
Table 1. Selected Bond Distances (Å) and Angles (deg) of 1a and 1
1a
1
d(Ti–Cl1)
d(Ti–Cl2)
(Cl1–Ti–Cl2)
d(Cp1centr–Ti)
d(Cp2centr–Ti)
(Cp1centr–Ti–Cp2
2.398(2) d(Ti–C11)
2.354(2) d(Ti–C12)
2.175(5)
2.186(5)
88.9(2)
2.079
2.059
133.35
(24) Sassmannshausen, J.; Green, J. C.; Stelzer, F.; Baumgartner, J.
Organometallics 2006, 25, 2796–2805.
92.15(8)
2.063
(C11–Ti–C12)
d(Cp1centr–Ti)
d(Cp2centr–Ti)
(Cp1centr–Ti–Cp2
(25) Sassmannshausen, J.; Track, A.; Stelzer, F. Organometallics 2006,
25, 4427–4432.
2.044
(26) Sassmannshausen, J.; Track, A.; Diaz, T. A. D. S. Eur. J. Inorg.
Chem. 2007, 16, 2327–2333.
)
131.45
)
centr
centr

1998 Organometallics, Vol. 27, No. 9, 2008
Sassmannshausen and Baumgartner
Table 2. 1H and 13C NMR Data of the Cationic Complexes 2, 3,
and 5
(Hf-CH2CH2CH2C5Me4) is 22.2(3) kcal/mol. He concluded that
“the sensitivity of the transition metal–carbon bond energy to s
character could be a reflection of considerable ionic (Mδ+-Cδ-)
bonding, since s character at carbon increases its electronega-
tivity.”
The proposed titanacycle thus formed should lead to a more
rigid ring system, with one methyl group of the CMe2 moiety
pointing toward the “back” of the molecule, leaving the other
to be more or less perpendicular to the substitute cyclopenta-
dienyl plane (cf. DFT section for a calculated structure). We
do observe a coordination of the methyl borate anion to 3 with
an unusual chemical shift of the coordinated methyl group at
–0.68 ppm. We observe a weak exchange with the free methyl
borate (EXSY), suggesting the presence of a second titanacyle
with the free coordination site probably occupied by the solvent
(4). Unfortunately, we did not obtain clear-cut evidence for this
OSIP. Solvent coordination of group 4 cationic metallocenes
has been observed before, most notably by Jordan31–33 and us
in the case of cationic zirconocene compounds.25
It is known from zirconocene chemistry that cationic zir-
conocene compounds can be stabilized by addition of aluminum
alkyls or excess starting material;34–36 thus, we reasoned this
route might also help the stabilization of the titanocene cation.
Indeed, we have demonstrated that the coordination of the
neutral starting material is in some cases preferred over the
coordination of the arene moiety.24 Thus, the reaction of 2 equiv
of 1 with 1 equiv of B(C6F5)3 in CD2Cl2 was monitored by
low-temperature NMR spectroscopy. At -60 °C, we observe
the familiar peaks for compound 2, with the tolyl peaks being
rather broad, indicating an exchange process. Additionally, peaks
attributed to compound 3 can be observed. The new peak at
-0.73 ppm is significant for the formation of the homodinuclear
compound 5. It is interesting to note that the formation of 5 is
not the major product, nor is 5 sufficiently stable to prevent
CH activation of the tolyl moiety. This is in contrast to the
reaction of 2 equiv of the zirconocene compound [(η5-
C5H4SiMe2tol)2ZrMe2] with 1 equiv of B(C6F5)3 in CD2Cl2,
which exclusively forms the homodinuclear zirconocene cation
[((η5-C5H4SiMe2tol)2ZrMe)2-µ-Me]+[MeB(C6F5)3]-.24 Mount-
ford and Clot recently investigated in great detail the reactivity
of cationic imido titanium alkyls.37,38 They noticed some unusual
activity of the cation toward the solvent CD2Cl2 and [(η5-
C5H5)2ZrMe2]. In both cases, solvent and C-H bond activation
was observed. The formation of adducts with AlMe3 and ZnMe2
was reported as well, including the solid-state structure of the
AlMe3 adduct.
OSIP.27 Complete assignments of all reported cationic com-
pounds are summarized in Table 2, and stacked plots of the
aromatic region of the discussed spectra are summarized in
Figure 3.
However, even gentle warming to -50 °C leads to a
decomposition of the product with concurrent formation of
methane. New peaks are growing in, suggesting the formation
of a new cationic titanocene compound, which we tentatively
assigned as the ISIP titanacycle [η5-C5H5-(η5:σ1-C5H4CMe2C6-
H3Me)Ti-µ-MeB(C6F5)3] (3) (cf. Figure 3). C-H bond activa-
tion of coordinated arenes to cationic titanium compounds has
been observed before, most notably recently by Hessen for half-
sandwich compounds.28 Bercaw investigated the relative bond
dissociation energies (BDE) of hafnocene and scandocene
hydrido compounds by thermal decomposition.29,30 The order
of relative bond dissociation energy is M-C(sp) > M-C(aryl)
> M-C(sp3). For example, in the case of the hafnocene hydride
[[η5-C5H5-(η5-C5H4CH2C6H5)HfH2] the ∆BDE for (Hf-H) and
(Hf-C6H5) is 0.8(3) kcal/mol, whereas that for (Hf-C6H5) and
Part II: DFT Calculations. An initial optimization of cation
2 from a starting structure similar to the previously reported
cationic compound [η5-Cp-(η5-C5H4CH2C6H5)ZrMe]+ (6)21
gave structure 7a (Figure 4). Resembling 6, structure 7a has a
(31) Sydora, O. L.; Kilyanek, S. M.; Jordan, R. F. Organometallics 2007,
26, 4746–4755.
(32) Stoebenau, E. J., III; Jordan, R. F. Organometallics 2006, 25, 3379–
3387.
(33) Wu, F.; Dash, A. K.; Jordan, R. F. J. Am. Chem. Soc. 2004, 126,
15360–15361.
(34) Bochmann, M.; Lancaster, S. J. Angew. Chem., Int. Ed. Engl. 1994,
33, 1634–1637.
(27) Horton, A. D.; deWith, J.; Linden, J. v. d.; Weg, H. v. d.
Organometallics 1996, 15, 2672–2674.
(35) Bochmann, M.; Lancaster, S. J. Organomet. Chem. 1995, 497, 55–
59.
(28) Deckers, P. J. W.; Hessen, B. Organometallics 2002, 21, 5564–
5575.
(36) Beck, S.; Prosenc, M.-H.; Brintzinger, H.-H.; Goretzki, R.; Herfert,
N.; Fink, G. J. Mol. Catal. A 1996, 111, 67–79.
(37) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. J. Am. Chem.
Soc. 2006, 128, 15005–15018.
(29) Bulls, A. R.; Schaefer, W. P.; Serfas, M.; Bercaw, J. E. Organo-
metallics 1987, 6, 1219–1226.
(30) Bulls, A. R.; Bercaw, J. E.; Manriquez, J. M.; Thompson, M. E.
Polyhedron 1988, 7, 1409–1428.
(38) Bolton, P. D.; Clot, E.; Adams, N.; Dubberley, S. R.; Cowley, A. R.;
Mountford, P. Organometallics 2006, 25, 2806–2825.

Synthesis of [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiMe]+
Organometallics, Vol. 27, No. 9, 2008 1999
Figure 3. NMR spectra of 1 with B(C6F5)3 in CD2Cl2, aromatic region. Italics are used for 3.
Figure 5. Bader analysis of 7a at the B3LYP/DZVP level.
Figure 4. Stationary points and schematic potential energy surface
for the phenyl rotation of cation 7. Relative energies are at the
B3LYP/ECP1 level.
Scheme 2. Proposed Intermolecular C-H Bond Activation,
Starting from 7b
close contact between the Ti and one of the ortho-carbons of
the tolyl ring (Figure 4).
The Ti-C1 distance of 2.63 Å is larger than the sum of
the van der Waals radii of Ti4+ (0.68 Å) and C4+ (0.16 Å).
The hydrogen attached to C1 of the tolyl ring is bent 9.7° out
of the plane of the tolyl ring, away from the titanium. The C-H
bond distance of 1.090 Å is only marginally longer than the
remaining C-H bonds in the arene moiety (1.084–1.087 Å).
Bader AIM analysis39 corroborates a nonagostic coordination:
a straight bonding path between the titanium and C1, with a
bond critical point bcp1 with an electron density F(r) ) 0.0243
and a Laplacian of the charge density of 32F(r) ) –0.01909
(Figure 5). For comparison, the values at the Ti-CH3 bond
critical point were determined to be F(r) ) 0.0972 and 32F(r)
) -0.02501. These values are slightly higher than the recently
computed values for zirconocene compounds.26
(Figure 4). This second minimum is slightly higher in energy
(6.1 kJ/mol) than 7a. A transition state, TS7, connecting these
two minima was located with a loose η3-coordination of the
phenyl ring. The distances between titanium and C1, C6, and
C5 are 3.52, 2.95, and 3.18 Å, respectively. As the resulting
barrier is only 24.0 kJ/mol (19 kJ/mol for TS6),21 scrambling
between 7a and 7b can be expected on the NMR time scale.
The Gibbs free energy of the transition state TS7 of ∆Gq )
24.30 kJ/mol indicates only a small change in entropy. As the
low-temperature NMR experiment indicated the formation of
methane concurrent with a change of the aromatic signals, we
explored the possibility of CH activation of the arene. Two
possible reaction pathways can be envisaged: the intramolecular
C-H bond activation, where the hydrogen of the arene moiety
is protonating the Ti-CH3 bond, and the intermolecular C-H
bond activation, where the hydrogen of the arene moiety is being
Further exploration of the potential energy surface revealed
the presence of at least one other minimum, wherein the titanium
is in close proximity to an ortho-carbon (7b, Ti-C5 2.58 Å)
with the attached hydrogen bent out of the Ph plane by 11.4°
(39) Bader, R. F. W. Atoms in Molecules: A Quantum Theory; Clarendon
Press: Oxford, UK, 1990.

2000 Organometallics, Vol. 27, No. 9, 2008
Sassmannshausen and Baumgartner
Figure 6. Stationary points and schematic potential energy surface for the CH activation of cation 7a. Relative energies are at the B3LYP/
ECP1 level.
expelled as a proton, rendering the organometallic compound
neutral (Scheme 2).
information of the bonding mode of the Ti-C bond, we
conducted a natural bonding orbital analysis (NBO). The bond
with the highest second order perturbation energy (452.8 kJ/
mol) is the interaction of the filled sp2.76 hybrid orbital on carbon
with the empty sd14.69 hybrid orbital on titanium. A second
bonding interaction (94.7 kJ/mol) can be found between the
same carbon hybrid orbital and an empty, nearly spherical
shaped sd0.26 hybrid orbital of titanium. Together with the
natural charge of this carbon of –0.548 from natural population
analysis, which is similar to an sp3-hybridized CH3 moiety
(ranging from -0.662 to -0.693), one can conclude a highly
polarized Tiδ+-Cδ- bond.30 Interesting is the interaction of the
π orbital of C-Cipso (p-p) with the p1d99.99 of titanium (81.6
kJ/mol), which is more of donor/acceptor character. Colored
plots of all discussed orbitals are available in the Supporting
Information. A similar analysis was performed for 8-anion. Here
we found a significant agostic interaction of the H-C-B bonds
with empty d orbitals of the titanium. The second-order
perturbation energy was calculated between 24.4 and 43.6 kJ/
mol. In particular the interaction between the CH66 bonding
sp3.04 orbital and the empty sp0.12d89.78 orbital of titanium was
calculated to be 43.6 kJ/mol. This is also reflected by the
distance between H and Ti of 2.43 Å. The second-order
perturbation energy of the CH70 bonding sp3.15 orbital and the
CH71 bonding sp3.49 orbital are 24.4 and 31.2 kJ/mol (Ti-H
bond distances: 2.66 and 2.16 Å), respectively. For comparison,
Marks41 reported the crystal structure of a binuclear constrained
geometry titanium cation with a Ti-H(C) bonding length
between 2.129 and 2.415 Å. Most interesting is an even stronger
interaction (83.8 kJ/mol) of the CH71 (in the metallocene wedge)
bonding sp3.49 orbital with the empty sd4.26 orbital of Ti. This
is reflected not only in the shorter Ti-H bond but also in Bader
analysis (Figure 7). We found a bond critical point BCP3 (F(r)
) 0.0338 and 32F(r) ) -0.0323) between the Ti-C bond,
which is slightly curved toward the carbon. Interestingly, we
found a BCP5 (F(r) ) 0.01364 and 32F(r) ) -0.0160) between
F and C and a BCP6 (F(r) ) 0.0147 and 32F(r) ) -0.0148)
between H71 and another F of the anion. Obviously, these
interactions help in stabilizing the hyperconjugated carbon.
Colored representations of the discussed orbitals are available
in the Supporting Information.
We investigated only the intramolecular activation, as this
appeared to be the most logical pathway. Starting from 7a, we
found a further minimum on the potential energy surface (8),
with a Ti-C(arom) bond. Both compounds 7a and 8 are
connected by the transition state TS7a-8 (Figure 6). The nature
of the transition state TS7a-8 was confirmed by frequency
analysis, with one negative frequency associated with the move
of the hydrogen from the arene to the methyl group, and was
further corroborated by IRC analysis.
The driving force for the reaction is the release of methane.
The calculated Gibbs free energy of ∆Gq(298.15 K) ) 89.7
kJ/mol (88.7 kJ/mol at 213.15 K) for the transition state TS7a-8
is significantly higher than the calculated free energy for TS7a-b
(∆Gq(298.15 K) ) 24.30 kJ/mol). As all these calculations were
basically done without the influence of the solvent, i.e., in the
gas phase, we were exploring the possibility of this influence
on the Gibbs free energy for the activation barrier. However,
including CH2Cl2 did not change the calculated activation energy
significantly. We can therefore conclude that the intramolecular
C-H bond activation is very unlikely to happen without any
additional factors, like for example the influence of the anion
or of catalytic amounts of B(C6F5)3, decreasing the energy
significantly. The coordination of B(C6F5)3 to cationic zir-
conocene compounds has been observed before.23 One possible
intermolecular reaction pathway could be that the anion is close
to the hydrogen of the coordinated arene carbon in 7b and thus
could abstract the proton readily (Scheme 2).
In order to corroborate our experimental NMR data, we
calculated the chemical shifts for compounds 7a, 7b, and 8.
For the CH-activated compound 8, we have furthermore replaced
the methane molecule with an empty coordination site (8a), with
the solvent CH2Cl2 (8-sol), with a chloride (8-Cl), with a
methide (8-Me), and with the anion [MeB(C6F5)3]- (8-anion).
All calculated chemical shifts and the corresponding structure
are summarized in Table 3.
Compound 8a was calculated as a symmetrical molecule with
a mirror plane parallel to the arene moiety.40 In order to obtain
(40) We have noticed that this calculated structure has a very shallow
PES, and a second structure with a bent arene arrangement and lower
symmetry could be obtained with the BP86 functional. As the energy
difference between both structures are negligible, we did not pursue this
any further.
(41) Li, H.; Li, L.; Marks, T. J.; Liable-Sands, L.; Rheingold, A. L.
J. Am. Chem. Soc. 2003, 125, 10788–10789.

Synthesis of [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiMe]+
Organometallics, Vol. 27, No. 9, 2008 2001
Table 3. Calculated Chemical Shifts of 7 and 8 at the B3LYP/NMR1 Level

2002 Organometallics, Vol. 27, No. 9, 2008
Sassmannshausen and Baumgartner
thawed, and stored in Young’s tap sealed ampules. All chemicals
were purchased from Aldrich and used as received.
NMR spectra were recorded on a Varian Gemini 200 or a Varian
UnityPlus 500 spectrometer and referenced to the residual protio
solvent peak for 1H. Chemical shifts are quoted in ppm relative to
tetramethylsilane. 13C NMR spectra were referenced with the
solvent peak relative to TMS and were proton decoupled using a
WALTZ sequence.
Computational Details. Density functional theory calculations
were carried out using the GAUSSIAN03, Revision C.02.42 program
package, running on a Debian Etch Linux Dual-Opteron or a Dual-
Xeon system, respectively. Geometries have fully been optimized
without symmetry constraints, involving the functional combinations
according to Becke43 (hybrid) and Lee, Yang, and Parr44 (denoted
B3LYP), with the corresponding valence basis set for Ti
(Stuttgart-Dresden, keyword SDD in Gaussian) and standard
6-31G* basis set45 for C, H, F, and B (denoted as ECP1). The
stationary points and transition states were characterized as minima
by analytical harmonic frequency (zero or one imaginary frequency,
respectively), which were used without scaling for zero-point and
thermal corrections.
Figure 7. Bader analysis of 8-anion, cut through the Ti -C-H77
plane with B and F slightly out of plane, at the B3LYP/DZVP level.
Table 4. Crystallographic Data of 1a and 1
1a
1
Magnetic shieldings σ have been evaluated for the B3LYP/ECP1
geometries using a recent implementation of the GIAO (gauge-
included atomic orbitals)-DFT method,46 involving the same
B3LYP level of theory, together with the recommended IGLO basis
II47 on C, H, F, and B. For Ti, an extended Wachters basis set was
used.48,49 This combination is denoted as NMR1. This approach
with this particular combination of functionals and basis sets has
proven to be quite effective for chemical shift computations for
transition metal complexes.21 1H and 13C chemical shifts have been
calculated relative to benzene as a primary reference and TMS for
comparison, with absolute shieldings for benzene σ(1H) 24.54 and
σ(13C) 47.83 and for TMS σ(1H) 31.73 and σ(13C) 177.59 with
the IGLO II basis set. The values for benzene were converted into
the TMS scale using the experimental δ values of benzene (7.26
and 128.5, respectively). Tables of Cartesian coordinates of all
calculated structures are available as electronic Supporting Informa-
tion (ESI) in x, y, z format. Bader and NBO5 analyses were
performed using the DZVP all-electron basis set on Ti50 and 6-31G*
for C, H, F, and B. Drawings of the electron charge density plots
were made using Aim2000.51 MOLDEN52 was used for the
chemical representation of the calculated compounds, and NBO-
View for the representation of the orbitals.53
empirical formula
Mw
TiCl2C20H22
381.18
100(2)
TiC22H28
340.34
100(2)
temperature [K]
size [mm]
cryst syst
space group
a [Å]
0.36 × 0.22 × 0.18 0.38 × 0.28 × 0.22
monoclinic
P2(1)/n
6.6105(2)
21.534(4)
12.248(2)
90
monoclinic
P2(1)/n
6.9748(2)
12.204(2)
21.448(4)
90
94.90(3)
90
1819(2)
4
b [Å]
c [Å]
R [deg]
ꢀ [deg]
93.12(3)
90
1741(5)
4
1.454
0.795
γ [deg]
3
V [Å
]
Z
Fcalc [g cm-3
]
1.243
0.469
728
absorp coeff [mm-1
F(000)
]
792
θ range
1.91 < θ < 24.00 1.91 < θ < 24.99
no. of reflns collected/unique 10 986/2722
12 620/3196
99.8
3196/0/213
1.04
R1 ) 0.079,
wR2 ) 0.161
R1 ) 0.090,
wR2 ) 0.168
0.70/-0.63
completeness to θ [%]
99.7
no. of data/restraints/params 2722/0/211
goodness of fit on F2
1.11
final R indices [I > 2σ(I)]
R1 ) 0.096,
wR2 ) 0.199
R1 ) 0.133,
wR2 ) 0.220
R indices (all data)
For the calculations including the solvent, the PCM model
implemented in Gaussian03 was used, together with the UFF, and
CH2Cl2 was chosen as a solvent. For X-ray structure analyses the
crystals were mounted onto the tip of glass fibers, and data
largest diff peak/hole [e-/ Å3] 1.01/-0.70
The calculated chemical shifts of 8-anion are in excellent
agreement with the observed chemical shifts. In particular, the
calculated high-field shift of the MeB of δ (ppm) -0.53, which
is indicative of the coordinated anion to the metal center, is in
excellent agreement with the observed chemical shift of δ (ppm)
-0.68. This high-field shift is due to the magnetic anisotropy
of the arene moiety in the titanacycle. Due to the observed
exchange between this coordinated methyl borate and the
noncoordinated methyl borate in the experiment, it is tempting
to speculate about the presence of a second titanacyle in solution,
probably with the free coordination site occupied by solvent
(8-sol). However, we did not obtain any clear-cut evidence for
this.
(42) Frisch, M. J.; et al. GAUSSIAN03, ReVision C.02; Gaussian, Inc.:
Pittsburgh, PA, 2004 (see Supplementary Information).
(43) Becke, A. D. J. Chem. Phys. 1993, 98, 5648–5642.
(44) Lee, C.; Yang, W.; Parr, R. G. Phys. ReV. B 1988, 37, 785–789.
(45) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56,
2257–2261.
(46) Cheeseman, J. R.; Trucks, G. W.; Keith, T. A.; Frisch, M. J.
J. Chem. Phys. 1996, 104, 5497–5509.
(47) Kutzelnigg, W.; Fleischer, U.; Schindler, M., NMR Basic Principles
and Progress; Springer-Verlag: Berlin, 1990; Vol. 23, pp 165–262.
(48) Bühl, M.; Mauschick, F. T. Magn. Reson. Chem. 2004, 42, 737–
744.
(49) Wachters, A. J. H. J. Chem. Phys. 1970, 52, 1033–1036.
(50) Godbout, N.; Salahub, D. R.; Andzelm, J. Can. J. Chem. 1992, 70,
560.
(51) Biegler-König, F.; Schönbohm, J.; Bayles, D. J. Comput. Chem.
2001, 22, 545–559.
Experimental Section
(52) Schaftenaar, G.; Noordik, J. H. Molden: a pre- and post-processing
program for molecular and electronic structures. J. Comput.-Aided Mol.
Des. 2000, 14, 123–134.
All experiments were carried out under a nitrogen atmosphere
using standard Schlenk techniques. Solvents were dried over sodium
(toluene, low in sulfur), sodium/potassium alloy (diethyl ether,
pentane), potassium (thf), and calcium hydride (dichloromethane).
NMR solvents were dried over activated molecular sieves, freeze
(53) Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.;
Bohmann, J. A.; Morales, C. M.; Weinhold, F. NBO 5.G.; Theoretical
Chemistry Institute: University of Wisconsin, Madison, WI, 2001.

Synthesis of [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiMe]+
Organometallics, Vol. 27, No. 9, 2008 2003
collection was performed with a Bruker-AXS SMART APEX CCD
for 3 h. The volatiles were removed under vacuum, and the residue
was extracted into pentane (3 times with 40 mL). Red crystals
suitable for X-ray analysis could be obtained by cooling the
concentrated extract to –30 °C.
diffractometer using graphite-monochromated Mo KR radiation
2
(0.71073 Å). The data were reduced to Fo and corrected for
absorption effects with SAINT54 and SADABS,54 respectively. The
structures were solved by direct methods and refined by a full-
matrix least-squares method (SHELXL97).54 If not noted otherwise
all non-hydrogen atoms were refined with anisotropic displacement
parameters. All hydrogen atoms were located in calculated positions
to correspond to standard bond lengths and angles. All hydrogen
atoms were omitted for clarity. Crystallographic data (excluding
structure factors) for the structures of compounds 1 and 2 reported
in this paper have been deposited with the Cambridge Crystal-
lographic Data Centre as supplementary publication no. CCDC
674039 (1a) and CCDC 674038 (1). Copies of the data can be
obtained free of charge on application to The Director, CCDC, 12
Union Road, Cambridge CB2 1EZ, UK [fax: (internat.) +44-1223/
336-033; e-mail: deposit@chemcrys.cam.ac.uk].
Yield: 0.78 g/2.2 mmol/28%. Anal. Found: C 77.60, H 8.23.
1
C22H28Ti requires: C 77.63, H 8.29. H NMR (CDCl3, 200 MHz,
20 °C): δ (ppm) –0.05 (s, 6H TiCH3); 1.51 (s, 6H, CCH3); 2.35 (s,
3H, PhCH3); 5.98 (s, 5H, Cp); 6.07 (m, 2H, Cp′); 6.12 (m, 2H,
Cp′); 7.14 (s, 2H, tolyl); 7.16 (s, 2H, tolyl). 13C NMR (CDCl3, 50
MHz, 20 °C): δ (ppm) 20.8 (PhCH3); 29.7 (CCH3); 39.6 (CCH3);
45.6 (TiCH3); 111.8 (Cp′); 113.6 (Cp); 114.1 (Cp′); 126.0 (tolyl);
128.7 (tolyl).
Conclusion
The titanocene compound [η5-C5H5-(η5-C5H4CMe2C6H4Me)-
TiMe2] (1), prepared from the titanocene dichloride precursor
[η5-C5H5-(η5-C5H4CMe2C6H4Me)TiCl2] (1a), reacts in CD2Cl2
at -60 °C with B(C6F5)3 to yield the outer sphere ion pair [η5-
C5H5-(η5:η1-C5H4CMe2C6H4Me)TiMe]+ (2) with a coordinated
tolyl group. Warming the sample to –50 °C leads to CH
activation of the coordinated arene ring and the formation of
the titanacycle [η5-C5H5-(η5:σ1-C5H4CMe2C6H3Me)Ti-µ-MeB-
(C6F5)3] (3), which is in exchange with an outer sphere ion pair
[η5-C5H5-(η5:σ1-C5H4CMe2C6H3Me)Ti]+ (4), and methane. The
structure of 4 could not be unambiguously assigned. Detailed
computational DFT studies support the formation of 2 and 3.
As previously reported, the coordination of the arene ring in 2
can be best described as nonagostic. Bader and NBO analyses
suggest the agostic coordination of the methyl borate to the
metal center in 3. Furthermore, the hyperconjugated carbon in
the methyl borate anion is further stabilized from a nearby
fluorine atom.
Preparation of [η5-C5H5-(η5-C5H4CMe2C6H4Me)TiCl2] (1a).
The compound 4-bromotoluene (4.32 g, 25.2 mmol) was slowly
added to a solution of n-butyllithium (10 mL, c ) 2.5 mol/L in
hexanes) in 200 mL of diethyl ether. The reaction mixture was
stirred for 1 h at ambient temperature and cooled to -78 °C. Next,
neat dimethylfulvene (2.6 g) was added. The white suspension was
slowly warmed to ambient temperature and stirred for 1 h. THF
(10 mL) was added, the resulting pale yellow solution was recooled
to -78 °C, and [η5-C5H5-TiCl3] (5.0 g, 25.2 mmol) was added.
The dark colored solution was slowly warmed to ambient temper-
ature and stirred for 2 days. The volatiles were removed under
vacuum, and the residue was extracted into dichloromethane.
Removing the volatiles under vacuum and washing the residue with
a small portion of pentane yielded 1a in pure quality. A sample
for elemental analysis was recrystallized from toluene, and the so-
obtained red needles were suitable for X-ray spectroscopy.
Yield: 6.0 g/62.5%/15.7 mmol. Anal. Found: C 63.06, H 5.71.
C20H22Cl2Ti requires: C 63.02, H 5.82. 1H NMR (CDCl3, 200 MHz,
20 °C): δ (ppm) 1.66 (s, 6H, CCH3); 2.42 (s, 3H, PhCH3); 6.24 (s,
5H Cp); 6.40 (t, 2H, Cp′); 6.57 (t, 2H, Cp′); 7.06 –7.08 (br, 4H,
-C6H4-). 13C NMR (CDCl3, 50 MHz, 20 °C): δ (ppm) 20.8
(PhCH3); 29.3 (CCH3); 40.6 (CCH3); 119.7 (Cp′); 120.1 (Cp′); 120.4
(Cp); 126.3 (m-C-tolyl); 128.9 (o-C-tolyl); 136.0 (i-C-PhMe); 145.7
(i-C-Cp); 146.4 (i-C-Cp).
Acknowledgment. J.S. thanks J. C. Green, M. Bühl, and
M. Flock for helpful discussions. We thank the IT department
for computational resources. Financial support from the Land
Steiermark, Österreich (county of Styria, Austria), is grate-
fully acknowledged.
Preparation of [η5-C5H4CMe2C6H4Me)TiMe2] (1). The com-
pound 1a (3.0 g, 7.8 mmol) was suspended in 100 mL of toluene,
and methyl lithium (9.8 mL, c ) 1.6 mol/L in diethyl ether) was
slowly added at 0 °C. The suspension was stirred at this temperature
Supporting Information Available: Tables of cartesian coor-
dinates of all calculated structures, (x, y, z format), colored NBO
plots and full citation of G03. This material is available free of
charge via the Internet at http://pubs.acs.org.
(54) Sheldrick, G. M. Acta Crystallogr. A 2008, A64, 112–122.
OM8000394