Preparation and reactions of base-free bis(1,3-di-tert- butylcyclopentadienyl)titanium, Cp′2Ti, and related compounds

Article abstract of DOI:10.1021/om7012315

The titanium(III) metallocene derivatives [1,3-(Me₃C) ₂C₅H₃]₂TiX, Cp′ ₂TiX, X = Cl, Me, H, OH, are prepared and shown to be monomelic with a d¹ electron configuration by solid state magnetic susceptibility studies over the temperature range 5-300 K. Reduction of the chloride by potassium amalgam in an argon atmosphere yields the base-free titanocene Cp′₂Ti, which is a spin triplet over the temperature range 5-300 K. In contrast, reduction in a nitrogen atmosphere gives the dimetal metallocene Cp′₂Ti(N₂)TiCp′₂, which shows a singlet-triplet equilibrium over the temperature range 5-300 K, which can be modeled by Heisenberg coupling with -2J = 210 cm^-1. The base-free titanocene reacts reversibly with H₂ or C₂H ₄ to give Cp′₂TiH₂ and Cp′₂Ti(C₂H₄), respectively. Both adducts are characterized by X-ray crystallography. The base-free titanocene reacts irreversibly with PhCCPh or N₂O to give Cp′ ₂Ti(PhCCPh) and Cp′₄Ti₂(μ-O), which are characterized by X-ray crystallography. In contrast Cp′₂Ti(C₂H₄) reacts with N₂O to give the bisoxo-bridged dimetal derivative Cp′₄Ti ₂(μ-O)₂.

Full text of DOI:10.1021/om7012315

Organometallics 2008, 27, 2959–2970
2959
Preparation and Reactions of Base-Free
Bis(1,3-di-tert-butylcyclopentadienyl)titanium, Cp′2Ti, and Related
Compounds
Marc D. Walter, Chadwick D. Sofield, and Richard A. Andersen*
Department of Chemistry and Chemical Sciences DiVision of Lawrence Berkeley National Laboratory,
UniVersity of California, Berkeley, California 94720
ReceiVed December 8, 2007
The titanium(III) metallocene derivatives [1,3-(Me3C)2C5H3]2TiX, Cp′2TiX, X ) Cl, Me, H, OH, are
prepared and shown to be monomeric with a d1 electron configuration by solid state magnetic susceptibility
studies over the temperature range 5–300 K. Reduction of the chloride by potassium amalgam in an
argon atmosphere yields the base-free titanocene Cp′2Ti, which is a spin triplet over the temperature
range 5–300 K. In contrast, reduction in a nitrogen atmosphere gives the dimetal metallocene
Cp′2Ti(N2)TiCp′2, which shows a singlet–triplet equilibrium over the temperature range 5–300 K, which
can be modeled by Heisenberg coupling with -2J ) 210 cm-1. The base-free titanocene reacts reversibly
with H2 or C2H4 to give Cp′2TiH2 and Cp′2Ti(C2H4), respectively. Both adducts are characterized by
X-ray crystallography. The base-free titanocene reacts irreversibly with PhCtCPh or N2O to give
Cp′2Ti(PhCtCPh) and Cp′4Ti2(µ-O), which are characterized by X-ray crystallography. In contrast
Cp′2Ti(C2H4) reacts with N2O to give the bisoxo-bridged dimetal derivative Cp′4Ti2(µ-O)2.
different chemistry than do the (C5Me5)2TiX or (C5Me5)2TiX2
derivatives. It is in this spirit of exploration that the studies
described in this paper were initiated.
Introduction
The 1,3-(Me3C)2C5H3 ligand, abbreviated Cp′ in this paper,
has not been used as extensively as the C5H5 (Cp) or the Me5C5
(Cp*) ligands in the preparation of metallocene derivatives of
the early d-transition metals. We have used it to prepare f-block
metallocenes since the [1,3-(Me3C)2C5H3]2M fragment is po-
tentially diastereotopic, a property that can be useful in dynamic
NMR studies.1 A possible reason for the lack of interest in the
1,3-(Me3C)2C5H3 ligand is that the chemical and physical
properties of, for example, Cp′2TiX2 or Cp′2TiX are likely to
be comparable to those of their Me5C5 analogues. Structurally
this is true, as shown by the bond distances and angles, when
X ) Cl, in the first four entries in Table 1. The major difference
in the four structures is that the ring(centroid)-Ti-ring(centroid)
angle is larger by 5–10° in the Me5C5 case, presumably a
reflection of the larger steric repulsion in the bent sandwich
structure with bulkier cyclopentadienyl ligands, while the TiCl
distances within each set are essentially equal. However, the
bond dissociation enthalpies (BDEs) of the group 4 metallocene
derivatives show that, for example, the Ti-I BDE of Cp′2TiI is
Results and Discussion
Synthesis, Properties, and Metathesis Reactions of
Cp′2TiCl. The preparation of Cp′2TiCl has been described
previously;2,3 our preparation using Cp′2Mg and TiCl3(thf)2 is
given in the Experimental Section. Cp′2TiCl shows a broad
resonance at δ 3.82 ppm (ν1/2 ) 430 Hz) in the 1H NMR
spectrum in C6D6 at 21 °C. It is monomeric in the solid state,
as shown by single-crystal X-ray diffraction (Table 1).3 Oxida-
tion with CCl4 or HgCl2 yields the known diamagnetic Cp′2TiCl2
(see Experimental Section for details).3,4
Addition of MeLi to Cp′2TiCl gives Cp′2TiMe, Scheme 1.
The monomethyl derivative is also obtained from the reaction
of Cp′2TiCl2 and 2 equiv of MeLi in good yield. As noted in
the Introduction, the bond dissociation enthalpy (BDE) of
Cp′2TiI is 11 kcal mol-1 less than that of (C5Me5)2TiI, and if
the lowered BDE is extrapolated to the Ti-Me bonds, it is not
surprising that Cp′2TiMe2 is not isolated. The green methyl
derivative is obtained by crystallization from hexane; it sublimes
at 60–70 °C in diffusion pump vacuum. The 1H NMR spectrum
consists of a broad resonance at 3.61 ppm (ν1/2 ) 430 Hz).
41 kcal mol-1, whereas that of (C5Me5)2TiI is 52 kcal mol-1 2
.
The weaker Ti-I bond extends to the BDEs of zirconium and
hafnium metallocene diiodides and dimethyls, which are about
20 kcal mol-1 weaker for Cp′2MX2 relative to those of
(C5Me5)2MX2. While the structural parity but thermochemical
disparity is doubtless due to several factors, steric effects are
probably the origin of the differences. Assuming that the
weakened Ti-I bond carries over to other Ti-X and TiX2 bonds
that are of more interest to organometallic chemists, such as
Ti-Me or Ti-H, these titanium derivatives might have rather
The methyl complex is converted, with degassed water, to
blue-purple Cp′2TiOH, mp 110–112 °C. The EI-mass spectrum
1
shows the molecular ion as the base peak, and the H NMR
spectrum consists of a broad resonance at 3.66 ppm (ν1/2
)
670 Hz). The IR spectrum exhibits a sharp absorption band due
to the νO-H stretch at 3668 cm-1, somewhat higher than found
in (C5Me5)2TiOH (νO-H ) 3652 cm-1).9
* To whom correspondence should be addressed. E-mail:
raandersen@lbl.gov.
(1) Lukens, W. W.; Beshouri, S. M.; Stuart, A. L.; Andersen, R. A.
Organometallics 1999, 18, 1247–1252.
(3) Urazowski, I. F.; Ponomaryov, V. I.; Ellert, O. G.; Nifant‘ev, I. E.;
Lemenovskii, D. A. J. Organomet. Chem. 1988, 356, 181–193.
(4) Okuda, J. J. Organomet. Chem. 1990, 385, C39–C42.
(2) King, W. A.; Di Bella, S.; Gulino, A.; Lanza, G.; Fragala, I. L.;
Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1999, 121, 355–366.
10.1021/om7012315 CCC: $40.75
2008 American Chemical Society
Publication on Web 05/23/2008

2960 Organometallics, Vol. 27, No. 13, 2008
Walter et al.
Scheme 1
Figure 1. Deuterium incorporation into the Cp′ ring in Cp′2TiD (9
atm, 6 days, atmosphere exchanged once). The ring deuterated
deuteride was crystallized from pentane at -65 °C and hydrolyzed
with H2O, and the hydrolysate was analyzed by GC-MS. The
simulation is based on the following isotopic distribution: C13D15H7
0.5%, C13D16H6 2.5%, C13D17H5 21.8%, and C13D18H4 75.2%.
In order to examine the acidity of the OH proton, its reactivity
toward Cp′2TiMe and D2 was investigated. It reacts with
Cp′2TiMe slowly at 65 °C to form CH4, HCp′, and a new
unidentified Ti(III)-containing compound in small yield, which
decomposes on further heating. The hydroxide decomposes
immediately in the presence of D2 (1 atm) to yield HCp′ and
unidentified organic compounds. No deuterium incorporation
into the Cp′ ring is found, as judged by the 2H NMR spectrum,
and the role of D2 in the reaction is unclear.
resonance by a factor of γH2/γD2) 42.5 based on the
Solomon-Bloembergen equation.12,13 The observed ratio of
23.3 in this case is less than the theoretical value; however this
is not unexpected, as most metal complexes exhibit smaller
ratios; for example, in Ti(acac)3 the ratio is on the order of 30.14
A resonance for Ti-D is not observed.
The reaction of Cp′2TiMe with H2 is different from that with
water. Thus, a red solution is formed immediately after exposing
a green pentane solution of Cp′2TiMe to 1 atm of H2, from
which Cp′2TiH may be crystallized at -80 °C as brick-red
Deuterium incorporation into CMe3 groups has been observed
1
blocks, mp 147–149 °C. The H NMR spectrum consists of a
previously in the case of [1,2,4-(Me3C)3C5H2]2CeH.15,16
A
broad resonance at 2.68 ppm (ν1/2 ) 140 Hz). Although the
hydride resonance cannot be located in the 1H NMR spectrum,
a strong TiH absorption (νTi-H) at 1550 cm-1 is observed in
the IR spectrum, which shifts to 1120 cm-1 when D2 is used in
the synthesis. This is in good agreement with the expected H/D
isotopic shift [νTi-H/νTi-D ) 1.38]. The monomeric hydrides
(C5Me5)2TiH and (C5Me4Ph)2TiH have νTi-H at 1490 and 1505
cm-1, respectively.10,11 Exposure to 1 atm of D2 at room
temperature not only yields the deuteride Cp′2TiD, but H/D
scrambling into the CMe3 groups of the Cp′ ring occurs, which
is also observed for (C5Me5)2TiH and (C5Me4Ph)2TiH.10,11
Upon exposure to high pressure of deuterium (9 atm) for 6
days, nearly complete deuterium incorporation into the CMe3
groups is achieved, as shown by the composition of the
molecular ion of Cp′D formed on hydrolysis with H2O (Figure
mechanism that accounts for deuterium incorporation is likely
to be similar; that is, the initially formed deuteride eliminates
HD from a methyl hydrogen of the CMe3 group, forming a
metallacycle. The metallacycle then reacts with additional D2
to re-form the deuteride with incorporation of deuterium into
the Cp′ ligand. The latter two steps proceed until deuterium
has been completely exchanged in the CMe3 groups. These steps
constitute an equilibrium process wherein D2 replaces HD due
to the much higher concentration of D2 in the reaction mixture.
Another remarkable property of Cp′2TiH is its thermochromic
behavior. When a pentane solution of Cp′2TiH under 1 atm of
N2 is cooled to -80 °C, it changes color from red to deep blue.
From EPR studies on (C5Me4Ph)2TiH, it is known that titani-
um hydride complexes can form nitrogen adducts, such as
(C5Me4Ph)2Ti(H)(N2),11 and therefore the color change might
be due to N2 complex formation. Subsequently, a pentane
solution of Cp′2TiH was exposed to 18 atm pressure of N2 and
alternatively to a mixture of 8 atm of N2 and 7 atm of H2;
however no reaction was observed. Cp′2TiH does not react with
C6F6, C6F5H, or C6F4H2 in C6D6 at room temperature or elevated
temperatures (65 °C). But on exposure to 1 atm of CO, a new
Ti(III)-containing compound is initially formed, which decom-
poses over time. After 6 h at 65 °C only resonances due to
HCp′ and Cp′2Ti(CO)2 can be identified; the carbonyl derivative
is described below.
2
1). This result is confirmed by H NMR spectroscopy, since
d36-Cp′2TiD exhibits a sharp resonance at 2.69 ppm (ν1/2 ) 6
Hz) in the 2H NMR spectrum due to the CMe3 groups. No H/D
scrambling into the methine positions is observed, which is
consistent with the GC-MS results. The 2H NMR resonance is
expected to be narrower than the corresponding 1H NMR
(5) McKenzie, T. C.; Sanner, R. D.; Bercaw, J. E. J. Organomet. Chem.
1975, 102, 457–466.
(6) Pattiasina, J. W.; Heeres, H. J.; van Bulhuis, F.; Meetsma, A.;
Teuben, J. H.; Spek, A. L. Organometallics 1987, 6, 1004–1010.
(7) Auburn, P. R.; Bercaw, J. E. J. Am. Chem. Soc. 1983, 105, 1136–
1143.
(8) Horacek, M.; Kupfer, V.; Thewalt, U.; Stepnicka, P.; Polasek, M.;
Mach, K. Organometallics 1999, 18, 3572–3578.
(9) Horacek, M.; Gyepes, R.; Kubista, J.; Mach, K. Inorg. Chem.
Commun. 2004, 7, 155–159.
(12) Bloembergen, N. J. Chem. Phys. 1957, 27, 572–573.
(13) Solomon, I. Phys. ReV. 1955, 99, 559–565.
(14) La Mar, G. N.; Horrocks, W. D.; Holm, R. H. NMR of Paramag-
netic Molecules; Academic Press: New York, 1973; pp 287–289; 638–640..
(15) Maron, L.; Werkema, E. L.; Perrin, L.; Eisenstein, O.; Andersen,
R. A. J. Am. Chem. Soc. 2005, 127, 279–292.
(10) Lukens, W. W.; Matsunaga, P. T.; Andersen, R. A. Organometallics
1998, 17, 5240.
(11) de Wolf, J. M.; Meetsma, A.; Teuben, J. H. Organometallics 1995,
14, 5466–5468.
(16) Werkema, E. L.; Messines, E.; Perrin, L.; Maron, L.; Eisenstein,
O.; Andersen, R. A. J. Am. Chem. Soc. 2005, 127, 7781–7795.

Base-Free Bis(1,3-di-tert-butylcyclopentadienyl)titanium
Organometallics, Vol. 27, No. 13, 2008 2961
titanocene crystals, and in spite of several attempts, no suitable
crystals for an X-ray diffraction experiment were obtained.22
A very broad resonance is observed in the 1H NMR spectrum
in C6D6 (30 °C) at 3.2 ppm (ν1/2 ) 300 Hz), presumably due to
the CMe3 groups, indicative of a paramagnetic compound; the
1
methine ring resonances are not observed. H NMR spectros-
copy is only moderately useful in these systems due to extreme
line broadening and a relatively limited chemical shift range
differentiating the Ti(II) and Ti(III) species (Table 2). A more
convenient way to detect Cp′2TiCl contamination, due to
incomplete reduction, is EPR and UV–vis spectroscopy, as these
physical methods are very sensitive to small amounts of
impurities. For this reason, EPR spectra of Cp′2Ti and Cp′2TiCl
solutions are recorded in toluene solution at room temperature.
However, Cp′2Ti does not give an EPR spectrum in toluene
solution at room temperature; (C5Me4SiMe3)2Ti is also EPR
silent.8 On the other hand, Cp′2TiCl gives a strong resonance
at gav ) 1.9677. The room-temperature UV–vis spectra consist
of broad absorptions in both of these metallocenes. Cp′2Ti has
its absorption at 589 nm (ꢀ ) 121 Lmol cm-1) probably due to
-1
Figure 2. ꢀm vs T plot for Cp′2TiX (X ) H, Me, OH, and H).
2
1
1
the spin-allowed e2g f e2g e2g transition, while Cp′2TiCl
exhibits two absorptions at 625 nm (ꢀ ) 96 L mol cm-1) and
560 nm (ꢀ ) 107 L mol cm-1), which are assigned to 1a1 f
2a1 and 1a1 f b1 transitions as in (C5Me5)2TiCl (Figure 3).23
Interestingly, the surface of Cp′2TiH changes color from red
to blue on prolonged exposure to a N2 atmosphere in the solid
state. When this blue material is dissolved in C6D6, a red solution
is obtained and no differences are noted in the 1H NMR spectra
relative to a sample of freshly prepared Cp′2TiH. Furthermore,
the IR spectrum recorded as a Nujol mull is identical to that of
the red material. The stability of Cp′2TiH toward N2 is quite
remarkable, compared to [1,3-(Me3Si)2C5H3]2TiH, abbreviated
as Cp′′2TiH, which in the presence of nitrogen reacts im-
mediately in C6D6 solution to form the known dinitrogen
-1
In the solid state, a plot of ꢀm vs T for Cp′2Ti is linear
from 5 to 300 K with µeff ) 2.44 µB (Figure 4).24 This value
is close to the solid state magnetic moment for (C5Me5)2Ti of
25
2.6 µB and the room-temperature solution moment of 2.4 µB
for (C5Me4SiMe2CMe3)2Ti.26 The magnetic moment of 2.44 µB
for Cp′2Ti implies that the titanocene has a triplet ground state
1
2
1
1
complex (Cp′′2Ti)2(N2), as identified by its IR and H NMR
with an electronic configuration of either e2g or e2g a1g (D5d
spectrum.17
symmetry).27,28
Solid State Magnetism (SQUID) of Cp′2TiX. Solid state
magnetism is a useful tool to distinguish between monomeric
and dimeric Ti(III) complexes. Monomeric Cp2TiX compounds
have one unpaired electron in an a1 orbital (in C2V molecular
symmetry),18 and the magnetic susceptibility obeys Curie law;
that is, the ꢀm-1 vs T plot is linear and the magnetic moment is
temperature independent and close to the spin-only value for a
S ) ½ system with µeff ) 1.73 µB. However, in dimeric
[Cp2TiX]2 complexes coupling between the spin centers is
Reactions of Cp′2Ti. 1. Dinitrogen. If the reduction of
Cp′2TiCl is performed under an atmosphere of N2, a 2:1
dinitrogen adduct (Cp′2Ti)2(N2) can be isolated by crystallization
from pentane as deep blue crystals with a metallic luster. The
same product is obtained on exposure of Cp′2Ti to N2. During
this process the color changes from a “dull” blue to deep blue;
even in the solid state the surface of the crystals perceptively
darken when exposed to even trace amounts of N2. As a powder,
the darkening of the surface is rapid. This and related reactions
of Cp′2Ti are shown in Scheme 2.
-1
observed; that is, the ꢀm-1 vs T plot is not linear.19–21 The ꢀm
vs T plots for a series of monomeric Cp′2TiX (X ) H, Me,
OH, Cl) are shown in Figure 2. They are linear from 5 to 300
K with µeff ≈ 1.7 µB, consistent with the expected S ) ½ ground
state (Table 2). The individual ꢀm-1 vs T and µeff vs T plots are
provided in the Supporting Information.
(22) We encountered similar problems with Cp′2V. However, crystals
of Cp′2Cr gave an excellent data set and a good X-ray structure. The Cp′2Cr
and Cp′2 Fe crystallize in an orthorhombic crystal lattice, whereas Cp′2Ti
and Cp′2V crystallize in a tetragonal lattice: Cp′2Ti: a ) 12.0614(11) Å, b
) 12.0614(11) Å, c )8.5317(11) Å, R ) ꢁ ) γ ) 90°; Cp′2V: a )
11.9810(11) Å, b ) 11.9810(11) Å, c ) 8.6312(11) Å, R ) ꢁ ) γ ) 90°;
Cp′2Cr: a ) 11.7750(6) Å, b ) 12.4122(6) Å, c )32.6410(20) Å, R ) ꢁ
) γ ) 90°, Pccn: Schultz, M. Acta Crystallogr. 2007, E63, m3085. Cp′2Fe:
a ) 11.561(2) Å, b ) 12.113(2) Å, c )33.437(6) Å, R ) ꢁ ) γ ) 90°,
Pccn: Boese, R.; Blaeser, D.; Kuhn, N. Z. Kristallogr. 1993, 205, 282–
284.
Synthesis and Properties of Cp′2Ti. The reduction of
Cp′2TiCl with various reducing agents was explored; the most
successful one was potassium amalgam in hexane under argon.
Blue crystals of Cp′2Ti were obtained from the mother liquor,
mp 148–149 °C. The titanocene sublimes at 60–70 °C under
diffusion pump vacuum, and it gives a molecular ion in the
mass spectrum. Due to the flat-plate-like morphology of the
(23) Lukens, W. W.; Smith, M. R.; Andersen, R. A. J. Am. Chem. Soc.
1996, 118, 1719–1728.
(24) The moment might be low due to the extreme sensitivity of the
base-free titanocene to trace amounts of N2 in argon even in the solid state.
This is particularly true for those samples that are finely ground, i.e., those
used for the magnetic susceptibility measurements.
(17) Hanna, T. E.; Keresztes, I.; Lobkovsky, E.; Bernskoetter, W. H.;
Chirik, P. J. Organometallics 2004, 23, 3448–3458.
(18) Lauher, J. W.; Hoffmann, R. J. Am. Chem. Soc. 1976, 98, 1729–
1742.
(25) Bercaw, J. E. J. Am. Chem. Soc. 1974, 96, 5087–5095, The value
of µeff varies from 2.60 µB at 298 K to 2.48 µB at 129 K. In footnote 32 of
ref 29, an effective magnetic moment of 2.15 µB is determined in the solid
state.
(19) Fieselmann, B. F.; Stucky, G. D. Inorg. Chem. 1978, 17, 2074–
2077.
(26) Hitchcock, P. B.; Kerton, F. M.; Lawless, G. A. J. Am. Chem. Soc.
1998, 120, 10264–10265.
(20) Jungst, R.; Sekutowski, D.; Davis, J.; Luly, M.; Stucky, G. D. Inorg.
Chem. 1977, 16, 1645–1655.
(27) Warren, K. D. Struct. Bonding (Berlin) 1976, 27, 45–159.
(28) Lever, A. B. P., Inorganic Electronic Spectroscopy; Elsevier:
Amsterdam, 1984; Chapter 7.
(21) Francesconi, L. C.; Corbin, D. R.; Hendrickson, D. N.; Stucky,
G. D. Inorg. Chem. 1979, 18, 3074–3080.

2962 Organometallics, Vol. 27, No. 13, 2008
Walter et al.
Table 1. Selected Bond Distances (Å) and Angles (deg) for Various Titanocene Complexes, Cp′ ) 1,3-(Me3C)2C5H3, Described in this Paper
compound
Ti-C(av) (Å)
Ti-Cp(cent) (Å)
Cp(cent)-Ti-Cp(cent) (deg)
Ti-X (Å)
other (Å)
a
(C5Me5)2TiCl2
2.44(2)
2.44(2)
2.39(1)
2.39(2)
2.44(3)
2.42(6)
2.41(4)
2.45(5)
2.37(1)
2.13
2.12
2.06
2.07
2.12
2.09
2.09
2.13
2.04
137
132
144
135
134
138
144
147
145
2.349(2)
2.349(1)
2.363(1)
2.337(1)
2.079(2)
2.169(6)
2.160(4)
2.167(4)
1.60(2)
b
Cp′2TiCl2
(C5Me5)2TiClc
b
Cp′2TiCl
d
Cp′2Ti(PhCtCPh)
CtC, 1.300(6)
CdC, 1.427(5)
CdC, 1.438(5)
CdC, 1.442(9)
d
Cp′2Ti(C2H4)
e
(C5Me5)2Ti(C2H4)
(C5Me4SiMe3)2Ti(C2H4)
f
d
Cp′2TiH2
a Ref 5. b Ref 3; there are several errors in Table 3 of this reference, the most serious of which is the Ti-C(av) distance in Cp′2TiCl2 is 2.435 (
0.019 Å, not 2.449 Å, and the Cp(cent)-Ti-Cp(cent) angle in Cp′2TiCl2 is 132°, not 121°. c Ref 6. d This work. e Ref 7. f Ref 8.
Table 2. Some Physical Properties of Cp′2Ti- and Cp′′2Ti-Containing Compounds, Cp′ ) 1,3-(Me3C)2C5H3 and Cp′′ ) 1,3-(Me3Si)2C5H3
compound
color
mp [°C]
1H NMRa
µeff (300 K) [µB]c
Cp′2TiCl
blue
green
blue-purple
red
blue
deep blue
blue
deep blue
red
145–146
128–129
110–112
147–149
148–149
130–140 (dec.)
153–154
143–144 (dec.)
223–225
3.82 (430)
3.61 (430)
3.66 (670)
2.68 (140)
3.2 (300)b
3.60 (60)
1.74
1.72
1.66
1.81
Cp′2TiMe
Cp′2TiOH
Cp′2TiH
Cp′2Ti
2.44
(Cp′2Ti)2(N2)
Cp′′2TiCl
(Cp′′2Ti)2(N2)
Cp′2TiCl2
1.46d
1.73
2.66 (340)
2.65 (170)
1.44d
diamagnetic
1.29 (s, 36H, CMe3)
5.81 (d, 4H, 4JCH) 3 Hz, ring-CH)
6.77 (t, 2H, 4JCH) 3 Hz, ring-CH)
1.06 (s, 36H, CMe3)
Cp′2Ti(C2H4)
yellow-green
122–123
diamagnetic
2.94 (s, 4H, C2H4)
4.34 (d, 4H, 4JCH) 2.4 Hz, ring-CH)
9.26 (t, 2H, 4JCH) 2.4 Hz, ring-CH)
1.17 (s, 36H, CMe3)
Cp′2Ti(CO)2
red
125–127
169–170
diamagnetic
diamagnetic
4.83 (d, 4H, 4JCH) 2 Hz, ring-CH)
5.13 (t, 2H, 4JCH) 2 Hz, ring-CH)
1.12 (s, 36H, CMe3)
Cp′2Ti(PhCCPh)
red-orange
5.51 (d, 4H, 4JCH) 2.6 Hz, ring-CH)
7.99 (t, 2H, 4JCH) 2.6 Hz, ring-CH)
6.89–7.11 (C6H5 resonances, overlapping 10H)
1.13 (s, 36H, CMe3)e
Cp′2TiH2
red
red
152–154 (dec)
228–229
diamagnetic
diamagnetic
2.62 (s, 2H, Ti-H)e
5.10 (d, 4H, 4JCH) 3 Hz, ring-CH)e
8.01 (t, 2H, 4JCH) 3 Hz, ring-CH)e
1.36 (s, 18H, CMe3)
(Cp′2TiO)2
1.45 (s, 18H, CMe3)
5.78 (d, 2H, 4JCH) 1.3 Hz, ring-CH)
6.04 (d, 2H, 4JCH) 2.7 Hz, ring-CH)
6.33 (t, 1H, 4JCH) 1.3 Hz, ring-CH)
6.53 (t, 1H, 4JCH) 2.7 Hz, ring-CH)
a Recorded in C6D6 at 21 °C, unless specified otherwise. The line width at half-peak height (Hz) for paramagnetic compounds is given in parentheses.
b Recorded in C6D6 at 30 °C. c The magnetic moment is given per titanium center and calculated from the value of ꢀT at 300 K using the relation µeff
2.828(ꢀT)0.5 d Strongly antiferromagnetically coupled Ti(III) centers. e Recorded in C7D8 at -54 °C.
)
.
The structure of the N2 complex is presumably related to those
of the C5Me5, 1,3-(Me3Si)2C5H3, Me4C5H, and Me4C5R (R )
iPr, tBu) analogues.17,29–31 It is noteworthy that (C5Me4-
SiMe3)2Ti8 and (C5Me4SiMe2CMe3)2Ti26 ignore dinitrogen at
1 atm pressure at room temperature, but at low temperatures
the base-free titanocenes (C5Me4R)2Ti (R ) SiMe3, SiMe2Ph,
CMe3, and CHMe2) reversibly bind N2 to form the 1:1 and 1:2
adducts (C5Me4R)2Ti(N2) and (C5Me4R)2Ti(N2)2, respectively.32,33
The dinitrogen adduct, (Cp′2Ti)2(N2), loses N2 when heated
in a sealed tube between 130 and 140 °C, as bubbles are
observed when the material melts, and in the inlet of the mass
spectrometer since the molecular ion is identical to that of the
base-free titanocene. Sublimation at 60–70 °C in a dynamic
diffusion pump vacuum also yields the base-free titanocene. The
UV–vis spectrum of (Cp′2Ti)2(N2) shows a very intense and
broad feature at 603 nm (ꢀ ) 1850 L mol cm-1) (Figure 3 and
Table 3).
The solid state magnetic susceptibility of the dinitrogen adduct
is of considerable interest relative to electron exchange behavior.
The 1/ꢀ vs T and ꢀ vs T plots are indicative of strong
antiferromagnetic coupling between the spin carriers, and the
corrected effective magnetic moment at room temperature is
2.07 µB per dimer (Figure 5). The magnetic data can be
simulated, assuming that two d1-spin carriers are coupled across
a (N2)2- bridge (Figure 6), using the Bleaney–Bowers equation
(eq 1).34,35 The singlet–triplet separation is equal to -2J, NR
represents the temperature-independent paramagnetism (TIP),
(29) Sanner, R. D.; Duggan, D. M.; McKenzie, T. C.; Marsh, R. E.;
Bercaw, J. E. J. Am. Chem. Soc. 1976, 98, 8358–8365.
(30) de Wolf, J. J.; Blaauw, R.; Meetsma, A.; Teuben, J. H.; Gyepes,
R.; Varga, V.; Mach, K.; Veldman, N.; Spek, A. L. Organometallics 1996,
15, 4977–4983.
(31) Hanna, T. E.; Bernskoetter, W. H.; Bouwkamp, M. W.; Lobkovsky,
E.; Chirik, P. J. Organometallics 2007, 26, 2431–2438.
(32) Hanna, T. E.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc. 2004,
126, 14688–14689.
(33) Hanna, T. E.; Lobkovsky, E.; Chirik, P. J. J. Am. Chem. Soc. 2006,
128, 6018–6019.
(34) Kahn, O., Molecular Magnetism; VCH: New York, 1993; pp 131–
132.

Base-Free Bis(1,3-di-tert-butylcyclopentadienyl)titanium
Organometallics, Vol. 27, No. 13, 2008 2963
Boltzmann statistics. The negative sign of 2J means that the
spins are antiferromagnetically coupled and the spin singlet is
lower in energy than the spin triplet.
The large value of -2J of 210 cm-1 is in contrast to the
magnetic studies on [(C5Me5)2Ti]2(N2), in which very little
exchange coupling was observed, and the effective magnetic
moment of 3.08 µB per dimer, or 2.18 µB per Ti, is temperature
invariant from 260 K to ca. 20 K. The value per Ti is
intermediate between 1.73 µB (spin-only value for Ti(III)) and
2.87 µB (spin-only value for Ti(II)). The absence of a signal in
the EPR spectrum was interpreted to be in agreement with a
linear Ti(II)NNTi(II) geometry, but the large negative orbital
Table 3. Optical Spectra of Some Titanocene Complexes
compound
λmax in nma
[1,3-(Me3C)2C5H3]2Ti
589 (121)
[1,3-(Me3C)2C5H3]2TiCl
{[1,3-(Me3C)2C5H3]2TiN}2
[1,3-(Me3Si)2C5H3]2TiCl
{[1,3-(Me3Si)2C5H3]2TiN}2
625 (96), 560 (107)
603 (1850)
617 (72), 550 (97)
614 (2500)
Figure 3. UV–vis spectra of Cp′2TiCl, Cp′2Ti, and (Cp′2Ti)2(N2)
in methylcyclohexane.
a λmax in nm in methylcyclohexane. Molar extinction coefficient is
given in parentheses in units of L mol-1 cm-1
.
-1
Figure 4. ꢀm vs T and µeff vs T plot for Cp′2Ti.
Figure 5. ꢀm-1 vs T and µeff (per dimer) vs T plot for (Cp′2Ti)2(N2).
Scheme 2
xp represents the amount of monomeric Ti(III) impurity and with
an assumed Curie constant, C, and the g value is determined in
a room-temperature solution EPR experiment.
2Ng2µ2B
2e2J ⁄ kT
C
T
ꢀm )
(1 - xp) +
xp + NR (1)
(
)
2J ⁄ kT
[
]
kT
1 + 3e
In this formalism, an equilibrium distribution between the
populations in the singlet and triplet state is described by
Figure 6. ꢀ vs T plot for (Cp′2Ti)2(N2). The g value was fixed as
the value obtained from the EPR study (gav ) 1.9785); the Curie
constant C was set to 0.3436 as determined from the ꢀ vs 1/T plot
of Cp′2TiCl. The parameters were obtained from a least-squares
refinement: J/k ) -152 K (-105 cm-1), xp) 5.6%, TIP 2.17 ×
10-4 cm3/mol, and -2J ) 304 K (210 cm-1).
(35) O’Connor, C. J., Magnetochemistry-Advances in Theory and
Experimentation. In Progress in Inorganic Chemistry; Lippard, S. J., Ed.;
J. Wiley & Sons: New York, 1982; Vol. 29, pp 203–285.

2964 Organometallics, Vol. 27, No. 13, 2008
Walter et al.
Figure 7. ꢀm-1 vs T and µeff (per dimer) vs T plot for (Cp′′2Ti)2(N2).
Figure 8. ꢀ vs T plot for (Cp′′2Ti)2(N2). The g value was fixed as
the value obtained from the EPR study (gav ) 1.9777); the Curie
constant C was set to 0.3298 as determined from the ꢀ vs 1/T plot
of Cp′′2TiCl. The parameters were obtained from a least-squares
refinement: J/k ) -144 K (-100 cm-1), xp) 3.4%, TIP 1.98 ×
10-4 cm3/mol, and -2J ) 288 K (200 cm-1).
contribution reducing the effective magnetic moment was
unexplained.29
The difference in the magnetic coupling between the titanium
centers in these two metallocene derivatives can be traced to
the orientation of the titanocene units relative to each other. A
recent theoretical calculation shows that the sign of the coupling
constant in the case of (Cp2Ti)2(µ-O) changes with the relative
orientation of the titanocene units.36 In [(C5Me5)2Ti]2(N2) the
two titanocene fragments are twisted by 90° with respect to each
other, and the molecule has D2d symmetry, treating the C5Me5
rings as points.29 Recently, Chirik reported the synthesis and
the solid state structure of {[(Me3Si)2C5H3]2Ti}2(N2), abbrevi-
ated as (Cp′′2Ti)2(N2).17 This complex is centrosymmetric, the
inversion center is located in the middle of the N-N bond, and
the idealized symmetry is D2h. A comparison between the solid
state magnetism of the structurally characterized (Cp′′2Ti)2(N2)
and (Cp′2Ti)2(N2) provides a test case of the hypothesis that
antiferromagnetic interactions between the spin centers is due
to the orientation of the titanocene fragments as suggested above.
Cp′′2TiCl is readily prepared from TiCl3(thf)3 and Cp′′2Mg (see
Experimental Section for details), and the solid state magnetism
is provided as Supporting Information. The reduction of
Cp′′2TiCl with potassium amalgam in boiling toluene under
dinitrogen yields the known complex (Cp′′2Ti)2(N2).17 The
UV–vis spectrum displays a very intense absorption at 614 nm
(ꢀ ) 2500 L mol cm-1) (see Supporting Information for details),
and the EPR spectrum at room temperature shows a resonance
at gav ) 1.9777.
Figure 9. Qualitative molecular orbital diagram for (Cp2Ti)2(N2)
in D2h symmetry.
The magnetism of (Cp′′2Ti)2(N2) closely resembles that of
(Cp′2Ti)2(N2) not only in the shape of the curve but also in the
singlet–triplet splitting, -2J, providing evidence that the mo-
lecular symmetry of these two complexes is the same, compare
Figures 5 and 6 with those of Figures 7 and 8. Qualitatively,
the antiferromagnetic coupling as observed in (Cp′′2Ti)2(N2) and
(Cp′2Ti)2(N2) can be explained by a simplified molecular orbital
from Cp′2Ti and one orbital from N2). A qualitative MO diagram
is shown in Figure 9.
In this model, bonding mainly occurs by way of the a1g lone
pair on N2 and the Cp′2Ti a1g symmetry orbitals, and the
π-donation and π-back-bonding are poor in these systems, which
stabilizes the b3u orbital, while the b2g orbital is slightly
destabilized. This qualitative model is supported by molecular
orbital calculations.37 The four metal-based electrons are located
in the b1u and b2g or b3u* orbital, leading to a small singlet–triplet
splitting and antiferromagnetic coupling between the spin
carriers as observed at low temperature in the solid state
magnetism (Figures 6 and 8). The required reorganization energy
model. For a molecule in D2h symmetry such as (Cp′′2Ti)2(N2)
2
and presumably (Cp′2Ti)2(N2), the filled orbitals of N2, (a1g
)
(a1u2) (b3u2, b2u2) (a1g2), in D2h symmetry combine with the
2
corresponding Cp′2Ti fragment orbitals.18 Only the (a1g
)
(corresponding to the 2σg orbital (lone pair) in D∞h symmetry
labels) has sufficient energy to combine with the metallocene
fragment orbitals, generating three orbitals (using two orbitals
(36) Ren, Q.; Chen, Z.; Ren, J.; Wei, H.; Feng, W.; Zhang, L. J. Phys.
Chem. A 2002, 106, 6161–6166.
(37) Blomberg, M. R. A.; Siegbahn, P. E. M. J. Am. Chem. Soc. 1993,
115, 6908–6915.

Base-Free Bis(1,3-di-tert-butylcyclopentadienyl)titanium
Organometallics, Vol. 27, No. 13, 2008 2965
sample is treated, i.e., if it was cooled and then heated or first
heated then cooled.38
Given the unusual behavior of (Cp′′2Ti)2(N2), the NMR
behavior of (Cp′2Ti)2(N2) was investigated. At room tempera-
ture, one dominant signal at 3.60 ppm (ν1/2 ) 60 Hz) is
observed, which overlaps a very broad resonance at 3.2 ppm
(ν1/2 ≈ 160 Hz). An exact integration is difficult, since the
resonances overlap, but it is on the order of 10:1. The ratio is
not strongly affected when the sample is prepared under argon
or nitrogen atmosphere. The chemical shifts are close to that of
base-free Cp′2Ti, and the absence of Cp′2TiCl is confirmed by
EPR spectroscopy. When the sample is heated to 373 K, the
signal at 3.2 ppm disappears, while the 3.6 ppm resonance shifts
to higher field. At 368 K, only one signal at 2.52 ppm (ν1/2
)
40 Hz) is detected, and on cooling, the original ratio is roughly
restored. Low-temperature NMR studies are problematic due
to the low solubility of both N2 adducts. Clearly, equilibria are
present in solution in both compounds, but given the time and
temperature dependence, a detailed molecular explanation is not
possible.38
2. Carbon Monoxide. Exposure of either the base-free or
the N2 adduct to CO yields Cp′2Ti(CO)2 as red crystals from
hexane. The adduct melts at 125–127 °C, gives a molecular
ion in the mass spectrum, and is diamagnetic, as deduced by
1
its H NMR spectrum; see Experimental Section for details.
Figure 10. Qualitative molecular orbital diagram for (Cp2Ti)2(N2)
in D2d symmetry.
The CO stretching frequencies are observed in the Nujol mull
IR spectrum at 1960 and 1880 cm-1. The corresponding
values for Cp2Ti(CO)2 and (C5Me5)2Ti(CO)2 are 1977 and
1899 cm-1 and 1940 and 1858 cm-1, respectively, consistent
with the view that the electron density39 on the metallocene
fragment in Cp′2Ti(CO)2 is intermediate between those of
the Cp and Cp* derivatives.40 The νCO values for the
dicarbonyl adducts [1,3-(Me3C)2C5H3]2Ti(CO)2 in Nujol and
[1,3-(Me3Si)2C5H3]2Ti(CO)2 in C6D6 are identical,17 although
they differ by 11 cm-1 in the corresponding zirconocene
adducts, with the Me3C derivatives being lower.40 The dicar-
bonyl takes on a blue coloration on standing in a dinitrogen
atmosphere for prolonged periods of time, presumably due to
slow displacement of CO by N2.
3. Diphenylacetylene. Addition of diphenylacetylene to the
titanocene gives the red, diamagnetic 1:1 adduct on crystalliza-
tion from hexane. The adduct does not react with N2 or ethylene
at 1 atm of pressure. An ORTEP diagram is shown in Figure
11, and some bond lengths and angles are listed in Table 1.
The bond distances and angles around the metallocene fragment
are very close to those of Cp′2TiCl2. In both metallocenes, the
Cp rings are eclipsed, and in the diphenylacetylene fragment
the phenyl rings are bent away from C(33) and C(34) by an
angle of 137° (averaged). The phenyl rings are twisted out of
the plane formed by Ti, C(33), and C(34); the two dihedral
angles formed by the intersections of the phenyl rings with the
is small, since the electrons are delocalized over three orbitals,
exhibiting only minor electron–electron repulsion. A qualita-
tive molecular orbital diagram for the D2d symmetric
[(C5Me5)2Ti]2(N2) is shown in Figure 10. In this case, the two
electrons reside in a degenerate e orbital; the electrons are
uncoupled and give rise to a spin triplet (S ) 1), for which a
magnetic moment of µeff ) 2.83 µB (per dimer) is expected.
This prediction is consistent with the magnetism observed for
[(C5Me5)2Ti]2(N2), which has a magnetic moment of 3.08 µB
(per dimer), and no electron exchange coupling from 20 to 260
K is observed.29 Thus, the magnetic results may be rationalized
by the symmetry of the metal-based fragment orbitals, which
are determined by the orientation of the metallocene fragments.
1
The H NMR spectrum of (Cp′′2Ti)2(N2) presents a puzzle,
since it is temperature and time dependent. A freshly crystallized
sample dissolved in C6D6 at 21 °C shows two resonances at
2.65 ppm (ν1/2 ) 160 Hz) and 5.3 ppm (ν1/2 ) 44 Hz), in the
intensity ratio 96:4 assigned to the SiMe3 groups. The freshly
crystallized sample of (Cp′′2Ti)2(N2) dissolved in C7D8, and
cooled to -30 °C, was exposed to dynamic vacuum, while flame
sealing the NMR tube. The NMR spectrum, collected at 290
K, contains the two signals in an intensity ratio of 87:13. Heating
the sample to 353 K results in both signals moving to high field;
however, the signal at 5.3 ppm gains intensity at the expense
of the signal at 2.65 ppm. At 348 K, the intensities are roughly
inverted compared to their ratio at 290 K. But, the original ratio
is not obtained on cooling to 288 K; the peak at 5.3 ppm remains
dominant, while the resonance at 2.65 ppm appears as two
separated signals, a very broad one at 2.73 ppm and a relatively
sharp one at 2.09 ppm, which overlaps with the toluene solvent
resonance. The intensity ratio of the 5.3 ppm resonance to the
2.73 and 2.09 ppm pair is 54:46. The origin of this unusual
behavior is unclear; however it can be reproduced using a freshly
prepared sample. The ratio is also influenced by the way the
(38) A referee suggested that the resonance at δ 2.65 may be assigned
to the D2h conformer and the one at δ 5.3 to the D2d conformer, since the
ratio irreversibly changes toward the δ 5.3 resonance, which is the least
sterically congested conformer. Over time, the resonance at δ 2.65 evolved
into two resonances, which might be due to various Cp′′ ring conformations
within the D2h conformation. While we agree with the general postulate
that isomers are present (see the next paragraph), we can provide no
experimental evidence for the specific assignment. The solid state magnetic
measurements might be useful, but they were obtained only to temperatures
of 300 K; on cooling from 300 to 5 K, no obvious deviation from the original
ꢀ vs T plots were evident to the eye. We thank a referee for this suggestion.
(39) Sikora, D. J.; Moriarty, K. J.; Rausch, M. D. Inorg. Synth. 1986,
24, 147–156.
(40) Zachmanoglou, C. E.; Docrat, A.; Bridgewater, B. M.; Parkin, G.;
Brandow, C. G.; Bercaw, J. E.; Jardine, C. N.; Lyall, M.; Green, J. C.;
Keister, J. B. J. Am. Chem. Soc. 2002, 124, 9525–9546.

2966 Organometallics, Vol. 27, No. 13, 2008
Walter et al.
Figure 12. ORTEP diagram of [1,3-(Me3C)2C5H3]2Ti(H2CCH2)
(30% probability ellipsoids). All hydrogen atoms were located; the
hydrogen atoms on the Me3C groups and methine positions of the
cyclopentadienyl ligand were included in calculated positions using
a riding model, but not refined. The hydrogen atoms are omitted
for clarity, except the hydrogen atoms on the ethylene ligand, which
were refined isotropically.
Figure 11. ORTEP diagram of [1,3-(Me3C)2C5H3]2Ti(PhCCPh)
(30% probability ellipsoids). Hydrogen atoms have been omitted
for clarity.
plane are 23° and 24°. The solid state structure is very simi-
lar to that found for Cp2Ti(PhCCSiMe3) and (C5Me5)Ti-
(PhCCSiMe3).41
4. Ethylene. Exposure of Cp′2Ti to ethylene (1 atm of
pressure) results in a rapid color change from blue to yellow,
and a green-yellow 1:1 adduct may be obtained from hexane
on cooling. The adduct melts at 122–123 °C, but does not yield
a molecular ion in the mass spectrum; only a molecular ion
due to Cp′2Ti is observed. The adduct is diamagnetic and has
1
averaged C2V symmetry by H and 13C NMR spectroscopy at
23 °C. When an excess of C2H4 is added to the C6D6 solution
of Cp′2Ti(C2H4), resonances due to the two individual compo-
nents are observed and no intermolecular exchange occurs on
the 1H NMR time scale. This is in contrast to (C5Me5)2Ti(C2H4),
which exchanges with added C2H4 at room temperature.42
Exposure of Cp′2Ti(C2H4) to 1 atm of N2 in C6D6 leads to a
Figure 13. ORTEP diagram of [1,3-(Me3C)2C5H3]2TiH2 (30%
probability ellipsoids). All of the hydrogen atoms were located;
the hydrogen atoms on the Me3C groups and methine positions of
the cyclopentadienyl ligand were included in calculated positions
using a riding model, but not refined. For clarity, all hydrogens are
omitted except the hydrides (H27, H28), which were refined
isotropically.
1
color change from yellow-green to blue-green, and in the H
NMR spectrum resonances of both species Cp′2Ti(C2H4) and
(Cp′2Ti)2(N2) can be detected in a ratio of approximately 10:1
at 20 °C.
at 152–154 °C, but no molecular ion is observed in the mass
spectrum, only that due to Cp′2Ti is observed. The IR spectrum
An ORTEP diagram of the ethylene adduct is shown in Figure
12, and important bond distances and angles are listed in Table
1. The molecular geometry is essentially identical to that of
(C5Me5)2Ti(C2H4)42 and close to that of (C5Me4SiMe3)2-
Ti(C2H4).8 The hydrogen atoms on the ethylene group were
located in the Fourier electron density map and refined isotro-
pically. This allows the bend angle, R, as defined by Stalick
and Ibers, of 60° to be calculated.43,44 This angle, the strong
bending observed in the diphenylacetylene adduct. and the νCO’s
in the CO adduct clearly indicate that the [1,3-(Me3C)2C5H3]2Ti
fragment is a good π-donor.
5. Dihydrogen. Perhaps the most interesting reaction of
Cp′2Ti is its reaction with dihydrogen. Exposure of Cp′2Ti in
C6D6 to an atmosphere of dihydrogen in an NMR tube results
in a rapid color change from blue to brown-red; exposure of
this solution to vacuum regenerates the blue color. This cycle
can be repeated several times. On a synthetic scale, cooling the
brown-red hexane solution to -80 °C yields dark red crystals
that are stable to vacuum in the solid state. The dihydride melts
shows a broad, strong feature at 1640 cm-1 assigned to νTi-H
,
since in (C5Me5)2TiH2, νTi-H is observed at 1560 cm-1 45
.
Crystals suitable for an X-ray diffraction study may be grown
from a dihydrogen-saturated solution of Cp′2Ti in hexane; an
ORTEP diagram is shown in Figure 13, and some bond distances
and angles are listed in Table 1. The hydrogen atoms, H(27
and 28), were located in the difference map and refined
isotropically. The orientation of the rings is staggered, as they
are in Cp′2Ti(PhCCPh), Figure 11. The Ti-H distances of
1.58(3) and 1.63(3) Å are comparable to the X-ray determined
distances of 1.69(5) and 1.84(4) Å for the two independent
(C5Me5)2TiH molecules,10 1.77(2) Å in (C5Me4Ph)2TiH,11 and
1.84(2) Å in the recently reported cation {(C5Me5)Ti-
[NP(CMe3)3][thf][H]}+.46 The HTiH angle of 72(2)° also seems
reasonable, since a HMoH angle of 75.5(3)° is found in
Cp2MoH2 in a neutron diffraction study.47
As mentioned above, Cp′2Ti undergoes a reversible color
change when exposed to H2, and this reaction may be monitored
(41) Burlakov, V. V.; Polyakov, A. V.; Yanovsky, A. L.; Struchkov,
Y. T.; Shur, V. B.; Volpin, M. E.; Rosenthal, U.; Görls, H. J. Organomet.
Chem. 1994, 476, 197–206.
(45) Bercaw, J. E.; Marvich, R. H.; Bell, L. G.; Brintzinger, H. H. J. Am.
Chem. Soc. 1972, 94, 1219–1238.
(42) Cohen, S. A.; Auburn, P. R.; Bercaw, J. E. J. Am. Chem. Soc. 1983,
105, 1136–1143.
(46) Ma, K.; Piers, W. E.; Gao, Y.; Parvez, M. J. Am. Chem. Soc. 2004,
126, 5668–5669.
(43) Stalick, J. K.; Ibers, J. A. J. Am. Chem. Soc. 1970, 92, 5333–5338.
(44) Ittel, S. D.; Ibers, J. A. AdV. Organomet. Chem. 1976, 14, 33–61.
(47) Schultz, A. J.; Stearly, K. L.; Williams, J. M.; Mink, R.; Stucky,
G. D. Inorg. Chem. 1977, 16, 3303.

Base-Free Bis(1,3-di-tert-butylcyclopentadienyl)titanium
Organometallics, Vol. 27, No. 13, 2008 2967
by 1H NMR spectroscopy. At 30 °C, the blue solution of Cp′2Ti
in C6D6 under argon shows a broad (ν1/2 ) 300 Hz) resonance
at δ 3.2 ppm. Exposure of this solution to an atmosphere of H2
results in a color change to brown-red and a slight upfield shift
in the broad resonance. Cooling the sample to -10 °C results
in the appearance of the broad resonance at δ 3.0 ppm, and
four sharp resonances without structure appear upfield. Cooling
to -55 °C results in the disappearance of the broad resonance,
the four sharp features due to Cp′2TiH2 appear at δ 1.13 (CMe3),
and the A2B ring resonances appear as a doublet at δ 5.10 (J )
3 Hz), a triplet at δ 8.01 (J ) 3 Hz), and a singlet at δ 2.62 due
to Ti-H increase in intensity. The chemical shift for the Ti-H
resonance is intermediate between δ 0.28 in (C5Me5)TiH245 and
δ 3.25 in (C5Me4iPr)2TiH2.48 Returning the sample to 30 °C
yields the original spectrum. This behavior implies an equilib-
rium, eq 2, which will have
Figure 14. Cp′ ring conformation in the Cp′4Ti2(µ-O)2 dimer.
oxide have been used as O-atom transfer reagents to prepare
monomeric, base-free titanocene oxides.57 Accordingly, the
reaction of Cp′2Ti and Cp′2Ti(C2H4) toward nitrous oxide, N2O,
was studied. On exposure of Cp′2Ti to N2O (1 atm of pressure)
the oxo-bridged dimetal compound Cp′4Ti2(µ-O) can be isolated,
albeit in low yield, and the molecular structure was determined
by X-ray diffraction.58 Under the same conditions (C5Me5)2Ti
yields a mixture of compounds, as indicated by 1H NMR spectros-
[1, 3 - (Me3C)2C5H3]2Ti + H2 h
[1, 3 - (Me3C)2C5H3]2 TiH2 (2)
a dependence on pressure of H2. Repeating the 1H NMR
experiment at 30 °C as a function of applied pressure of H2
results in an upfield shift of the averaged chemical shift of the
broadened resonance, presumably due to the averaged chemical
shift of CMe3 groups, until a sharp feature begins to appear at
δ 1.5 at an applied pressure of about 30 psi, which sharpens
and shifts upfield as the applied pressure is increased to about
160 psi. These shifts as a function of applied pressures are shown
graphically as Supporting Information. The qualitative pressure
dependence is consistent with the equilibrium reaction shown
in eq 2. Unfortunately, the equilibrium reaction can be treated
only semiquantitatively since, although the absolute chemical
shifts of pure Cp′2Ti or Cp′2TiH2 are known accurately at a
given temperature, that due to paramagnetic Cp′2Ti is very broad
and temperature dependent. The dependence of the equilibrium
on the applied pressure of H2 may be estimated from the ratios
of the populations of the two titanocenes and the solubility of
H2 at 30 °C in toluene,49 as Kp(303 K) ) 29.1(2) bar-1 (see
Supporting Information for details). For (C5Me5)2Ti a value of
Kp(300 K) ≈ 100 bar-1 was determined,45 which is consistent
with the notion that the Cp′2Ti binds H2 less strongly than does
the (C5Me5)2Ti fragment.
copy;resonancesdueto[(C5Me5)Ti]2[µ-(η1:η5-CH2C5Me4)](µ-O)253,54
59,60
and for (C5Me5)4Ti4(µ-O)6
can be identified. Monomeric
(C5Me5)2Ti(O)(py) may be isolated, if the reaction of (C5Me5)2Ti
or (C5Me5)2Ti(C2H4) with N2O is conducted in the presence of
pyridine.61 However, on exposure of Cp′2Ti(C2H4) to N2O (1
atm of pressure), the only identifiable product is the dimeric
Cp′4Ti2(µ-O)2, mp 228–229 °C. Cp′4Ti2(µ-O) is not obtained
by this synthetic methodology, since addition of 0.5 equiv of
N2O to a pentane solution of Cp′2Ti(C2H4) yields a mixture of
Cp′4Ti2(µ-O)2 and unreacted starting material. Although the
microcrystalline nature of Cp′4Ti2(µ-O)2 precluded a crystal
structure analysis, the 1H NMR data are consistent with a
dimeric molecule of C2h symmetry. Furthermore, its IR spectrum
resembles that of the uranium analogue Cp′4U2(µ-O)2, for which
1
single-crystal and EXAFS data are available.1 The H NMR
spectrum consequently shows inequivalent Cp′ resonances (see
Experimental Section), suggesting that the geometrical structure
shown in Figure 14 is analogous to that found for its uranium
analogue.
Cp′4Ti2(µ-O)2 does not react with excess Cp′2Ti(C2H4) or
4-dimethylaminopyridine (DMAP), suggesting that the dimer
does not dissociate, consistent with its 1H NMR spectrum.
Similar observations have been reported for Cp′′4Ti2(µ-O)2,
which was prepared from Cp′′2TidNR and Ph2CO.17
The reversible reaction illustrated in eq 2 is of synthetic utility,
since the purest form of Cp′2Ti is obtained by allowing
crystalline Cp′2TiH2 to decompose by gently warming a solution
in hexane, which is in contrast to the published observations
25
on (C5Me5)2TiH2 and (C5Me4iPr)2TiH2;48 in both of these
cases H2 elimination leads to the formation of Ti(III) hydrides.
6. N2O. Synthesis and reactions of metal oxides and hydrox-
ide complexes have been of interest to us in recent years.1,50–52
Nitrous oxide is a convenient source of oxygen atoms for the
synthesis of oxometallocenes (and the products derived there-
from) as well as for the insertion into metal-hydrogen and
-carbon bonds.53–56 Alternatively, ethylene oxide or styrene
Conclusions
The introduction of the 1,3-di-tert-butylcyclopentadienyl
ligand into titanium chemistry allows the isolation of base-free
(54) Bottomley, F.; Lin, I. J. B.; White, P. S. J. Am. Chem. Soc. 1981,
103, 703–704.
(55) Bottomley, F.; Lin, I. J. B.; Mukaida, M. J. Am. Chem. Soc. 1980,
102, 5238–5242.
(48) Hanna, T. E.; Lobkovsky, E.; Chirik, P. J. Eur. J. Inorg. Chem.
2007, 2677–2685.
(56) Matsunaga, P. T.; Morropoulos, J. C.; Hillhouse, G. L. Polyhedron
1995, 14, 175–185, and references therein.
(49) Lühring, P.; Schumpe, A. J. Chem. Eng. Data 1989, 34, 250–252.
(50) Polse, J. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.
1995, 117, 5393–5394.
(57) Hanna, T. E.; Lobkovsky, E.; Chirik, P. J. Inorg. Chem. 2007, 46,
2358–2361.
(58) Sofield, C. D.; Walter, M. D.; Andersen, R. A. Acta Crystallogr. E
2004, 60, m1417–m1419.
(51) Schwartz, D. J.; Smith, M. R.; Andersen, R. A. Organometallics
1996, 15, 1446–1450.
(59) Babcock, L. M.; Day, V. W.; Klemperer, W. G. J. Chem. Soc.,
Chem. Commun. 1987, 858.
(52) Zi, G.; Li, J.; Werkema, E. L.; Walter, M. D.; Gottfriedsen, J. P.;
Andersen, R. A. Organometallics 2005, 24, 4251–4264.
(53) Bottomley, F.; Egharevba, G. O.; Lin, I. J. B.; White, P. S.
Organometallics 1985, 4, 550–553.
(60) Babcock, L. M.; Klemperer, W. G. Inorg. Chem. 1989, 28, 2003.
(61) Smith, M. R.; Matsunaga, P. T.; Andersen, R. A. J. Am. Chem.
Soc. 1993, 115, 7049–7050.

2968 Organometallics, Vol. 27, No. 13, 2008
Walter et al.
mmol) was added to the blue solution using a syringe. The solution
immediately turned green, and a colorless solid precipitated. The
solvent was removed under reduced pressure and the green solid
was extracted with hexane (50 mL). The solution was filtered,
concentrated to a volume of 25 mL, and cooled to -20 °C. The
green crystals (1.24 g) were isolated by filtration, and the mother
liquor was concentrated and cooled to -80 °C. Total yield: 2.14 g
(58%). The isolated crystals gave negative Li flame and negative
AgNO3 tests. Purification can also be accomplished by sublimation
in diffusion pump vacuum at 60–70 °C. Mp: 128–129 °C (rev). 1H
NMR (C6D6, 21 °C): δ 3.61 (ν1/2 ) 430 Hz). IR (Nujol mull; CsI
windows, cm-1): 1297(w), 1252(s), 1238(w), 1200(m), 1168(m),
1108(w), 1062(m), 1023(m), 939(m), 931(m), 844(s), 820(w),
812(w), 802(m), 791(s), 721(w), 680(w), 658(s), 605(w), 495(w),
442(w), 387(w), 310(w). Anal. Calcd for C27H45Ti: C, 77.7; H,
10.86. Found: C, 77.58; H, 11.13.
Cp′2Ti, which reacts with a variety of substrates in analogy with
(C5Me5)2Ti. The purity of the base-free titanocene can easily
be determined by EPR and UV–vis spectroscopy. The reaction
with N2 gives the 2:1 complex (Cp′2Ti)2(N2), in which the
titanium centers are strongly antiferromagnetically coupled.
Although a crystal structure was not obtained, the magnetic
behavior is essentially identical to its (Cp′′2Ti)2(N2) analogue,
whose X-ray crystal structure is known, in which the two
titanocene units are related by inversion with the inversion center
located in the middle of the N-N bond; this allows effective
antiferromagnetic coupling via the N2 bridge. This is in contrast
to Bercaw’s observations on [(C5Me5)2Ti]2(N2), in which the
titanium centers are twisted by 90° relative to each other, and
consequently only weak coupling is allowed. Cp′2Ti(C2H4),
which is generated from Cp′2Ti and C2H4, is a convenient
starting material for the synthesis of dimeric Cp′4Ti2(µ-O)2
species with C2h symmetry, as judged from its 1H NMR
spectrum. Cp′2TiCl can be functionalized with MeLi to give
Cp′2TiMe, which reacts with H2 and H2O to yield monomeric
Cp′2TiH and Cp′2TiOH, respectively.
An alternative method: Methyllithium (11 mL, 0.81 M in Et2O,
8.8 mmol) was added dropwise to an ether suspension of Cp′2TiCl2
(2.0 g, 4.2 mmol). The dark red suspension changed to a light green
with a colorless precipitate. The mixture was stirred for 30 min,
and the solvent was removed under reduced pressure. The solid
was extracted with hexane (100 mL), and the green solution was
filtered and concentrated to a volume of 40 mL and cooled to -80
°C. Green needles of Cp′2TiMe were isolated (identified by its IR
spectrum and mp).
Cp′2TiOH. Toluene (50 mL) was added to Cp′2TiMe (1.3 g,
3.1 mmol). A solution of degassed water (56 µL, 3.1 mmol) in 30
mL of tetrahydrofuran was added to the green Cp′2TiMe solution
via cannula. The mixture was heated gently to 35–40 °C for 15
min. During this time the color changed to light blue-purple and
gas evolved. The solvent was removed under reduced pressure, and
the residue was extracted into pentane (30 mL). The pentane
solution was concentrated and cooled to -25 °C to give blue-purple
blocks (0.73 g, 1.74 mmol, 56%). Mp: 110–112 °C (rev). 1H NMR
(C6D6, 21 °C): δ 3.66 (ν1/2 ) 670 Hz). IR (Nujol mull; CsI windows,
cm-1): 3668(s), 3080(w), 1595(w), 1392sh.(m), 1375(s), 1360(s),
1300(w), 1258(s), 1205(m), 1170(m), 1090(vbr m), 1060(vbr m),
1030(vbr m), 940(vbr m), 890(br w), 855(m), 842(vs), 815(m),
796(s), 730(vbr.w), 690(w), 680(w), 660(m), 630(br w), 590′(br
vs), 595(sh), 500(w), 445(vbr m), 390(m), 340(w). Anal. Calcd for
C26H43TiO: C, 74.44; H, 10.33. Found: C, 74.63; H, 10.59. The EI
mass spectrum showed a parent ion at m/e ) 419 amu. The parent
ion isotopic cluster was simulated (calcd %, obsvd %): 417 (10,
9), 418 (13, 12), 419 (100, 100), 420 (37, 37), 421 (14, 14), 422
(3, 3).
Cp′2TiH. Hexane (50 mL) was added to Cp′2TiMe (1.3 g, 3.1
mmol), and the green solution was exposed to 1 atm of hydrogen.
The solution turned dark red in color within 5 min. The volume of
the solution was reduced to 10 mL. Slow cooling to -80 °C under
a nitrogen atmosphere yielded brick-red crystals (1.04 g, 2.57 mmol,
83% yield). Solutions of Cp′2TiH show thermochromic behavior;
they are red at room temperature and deep blue at -80 °C. Mp:
147–149 °C (rev). 1H NMR (C6D6, 21 °C): δ 2.68 (ν1/2 ) 140
Hz). IR (Nujol mull; CsI windows, cm-1): 1550(s) (Ti-H), 1375(s),
1355(s), 1297(m), 1233(w), 1200(m), 1165(m), 1050(m), 1025(w),
945(w), 935(w), 927(m), 852(w), 837(s), 810(m), 781(w), 772(m),
723(m), 690(m), 659(m), 610(w), 585(w), 500(w), 470(m), 397(m),
320(w), 250(w). Anal. Calcd for C26H43Ti: C, 77.39; H, 10.74.
Found: C, 77.22; H, 10.92.
Experimental Section
General Comments. All reactions, product manipulations, and
physical studies have been carried out as previously described.10,62–65
Cp′2TiCl. Tetrahydrofuran (150 mL) was added to a mixture of
TiCl3 · 3THF (13.0 g, 34.9 mmol) and Cp′2Mg (13.2 g, 34.9 mmol).
The solution turned dark blue immediately, and the mixture was
stirred for 12 h. The solvent was removed under reduced pressure,
and the resulting dark blue solid was extracted with 2 × 150 mL
of hexane. The combined extracts were concentrated to a volume
of 200 mL and cooled to -80 °C. Blue needles were isolated (11.6
1
g, 83% yield). Mp: 145–146 °C. H NMR (C6D6, 21 °C): δ 3.8
(ν1/2 ) 430 Hz). IR (Nujol mull; CsI windows; cm-1): 3110(w),
3090(w), 1393(m), 1372(s), 1364(m), 1357(s), 1294(m), 1253(s),
1197(m), 1166(m), 1059(s), 1035(w), 1028(w), 935(w), 928(w),
919(w), 885(w), 878(w), 846(s), 821(w), 808(m), 720(w), 680(w),
655(m), 498(m), 453(m),, 342(w), 325(w), 274(m). UV–vis (me-
thylcyclohexane, 25 °C): 625 nm (ꢀ ) 96 L mol · cm-1), 560 nm
(ꢀ ) 107 L mol · cm-1). Anal. Calcd for C26H42ClTi: C, 71.31; H,
9.67. Found: C, 71.04; H, 9.57. The EI mass spectrum showed a
parent ion at m/e ) 437 amu. The parent ion isotopic cluster was
simulated (calcd %, obsvd %): 435 (10, 13), 436 (12, 15), 437 (100,
100), 438 (44, 47), 439 (53, 44), 440 (14, 17), 441 (5, 5), 442 (1, 1).
Cp′2TiCl2. Carbon tetrachloride (5 mL, 50 mmol) was dissolved
in tetrahydrofuran (100 mL), and the solution was added to Cp′2TiCl
(4.48 g, 10.2 mmol) and stirred for 8 h. The dark blue solution
gradually changed to red, and red needles deposited, which were
1
collected (4.32 g, 89% yield). Mp: 223–225 °C. H NMR (C6D6,
4
21 °C): δ 1.29 ((s), 36 H, C(CH3)3), 5.81 (d, 4H, JCH ) 3 Hz,
4
ring-CH), 6.77 ppm (t, 2H, JCH ) 3 Hz, ring-CH).
A second method: Tetrahydrofuran (250 mL) was added to
mixture of Cp′2TiCl (7.33 g, 16.7 mmol) and HgCl2 (5.00 g, 18.4
mmol). A dark red solution with a colorless precipitate immediately
formed. The mixture was stirred for 3 h, and the solvent was
removed under reduced pressure. The dark red product was
sublimed (150 °C, 10-3 Torr) and crystallized from tetrahydrofuran.
The compound has been prepared by other methods.3,4
Cp′2TiMe. Diethyl ether (50 mL) was added to Cp′2TiCl (3.9
g, 8.8 mmol). Methyllithium in diethyl ether (11 mL, 0.81 M, 8.8
(Cp′-d18)2TiD. Pentane (50 mL) was added to Cp′2TiMe (0.3 g,
0.72 mmol), and the green solution was exposed to 9 atm of D2
for 6 days; the atmosphere was exchanged once during this time
period. The solution turned dark red in color within 5 min. The
volume of the solution was reduced to 10 mL. Slow cooling to
-80 °C under an nitrogen atmosphere yielded brick-red crystals
(62) Schultz, M.; Boncella, J. M.; Berg, D. J.; Tilley, T. D.; Andersen,
R. A. Organometallics 2002, 21, 460–472.
(63) Walter, M. D.; Schultz, M.; Andersen, R. A. New J. Chem. 2006,
30, 238–246.
(64) Walter, M. D.; Berg, D. J.; Andersen, R. A. Organometallics 2006,
25, 3228–3237.
2
(0.2 g). H NMR (C6D6/C6H6, 21 °C): δ 2.69 (ν1/2 ) 5 Hz). IR
(65) Lukens, W. W.; Andersen, R. A. Inorg. Chem. 1995, 34, 3440–
3443.
(Nujol mull; CsI windows, cm-1): 3080(w), 2210(vs) (C-D),

Base-Free Bis(1,3-di-tert-butylcyclopentadienyl)titanium
Organometallics, Vol. 27, No. 13, 2008 2969
2110(br m) (C-D), 2060(m) (C-D), 2040(m) (C-D), 1530(vbr m),
1460(s), 1378(s), 1290(w), 1260(w), 1215(s), 1170(m), 1120(s) (Ti-
D), 1100(w), 1052(w), 1025(m), 912(w), 902(m), 845(vs), 838(sh),
818(w), 780(vs), 750(m), 710(w), 707(w), 672(m), 648(m), 600(vw),
482(m), 467(m).
1330(m), 1250(vbr s), 1210(vs), 1187(w), 1095(vs), 1070(m),
1060(s), 932(sh), 922(s), 870(s), 850(vbr s), 760(vs), 698v(s),
638v(s), 490(s), 438(s), 412(s), 383(s), 370(s), 350(vw), 300(s),
280(s), 258(m), 250(s). UV–vis (methylcyclohexane, 25 °C): 617
nm (ꢀ ) 72 L mol · cm-1), 550 nm (ꢀ ) 97 L mol · cm-1). Anal.
Calcd for C22H42Si4ClTi: C, 52.61; H, 8.43. Found: C, 52.33; H,
8.52.
Cp′2Ti. Under argon, potassium amalgam was prepared from
20 mL of mercury and potassium (4.6 g, 120 mmol). Cp′2TiCl (10.3
g, 23.5 mmol) was dissolved in hexane (200 mL), and the solution
was added to the potassium amalgam. The mixture was heated to
reflux and stirred for 12 h. The stirring was halted, and the mixture
was allowed to cool to room temperature. The dark blue solution
was filtered and concentrated to a volume of 100 mL. Layered
crystals formed (3.85 g, 41% yield). A second crop of crystals was
obtained by concentrating and cooling the solution to -80 °C (2.5
g, 67% overall yield). Using the silver nitrate test, no chloride was
detected either in the crystals or in mother liquor. Mp: 148–149
°C. 1H NMR (C6D6, 30 °C): δ 3.2 (ν1/2 ) 300 Hz). IR (Nujol mull;
CsI windows, cm-1): 3105(w), 3095(m), 1489(m), 1413(m),
1382(m), 1369(s), 1362(s), 1354(w), 1318(w), 1315(w), 1271(w),
1253(s), 1202(m), 1187(s), 1098(s), 1070(m), 1061(m), 1029(m),
948(s), 923(s), 904(w), 899(w), 867(s), 835(s), 760(s), 728(w),
700(m), 682(w), 673(w), 640(m), 591(w), 495(w), 470(w), 440(s),
420(m), 410(s), 377(w), 365(w), 338(w), 268(s). UV–vis (meth-
ylcyclohexane, 25 °C): 589 nm (ꢀ ) 121 L mol · cm-1). Anal. Calcd
for C26H42Ti: C, 77.59; H, 10.52. Found: C, 77.29; H, 10.29. The
EI mass spectrum showed a parent ion at m/e ) 402 amu. The
parent ion isotopic cluster was simulated (calcd %, obsvd %): 405
(3, 3), 404 (13, 17), 403 (36, 45), 402 (100, 100), 401 (13, 17),
400 (11, 14), 399 (0, 2).
(Cp′′2Ti)2(N2). Under nitrogen, potassium amalgam was prepared
from 5 mL of mercury and potassium (1.2 g, 31 mmol). Cp′′2TiCl
(2.95 g, 5.88 mmol) was dissolved in toluene (60 mL), and the
solution was added to potassium amalgam. The mixture was heated
to reflux and stirred for 12 h. The stirring was halted, and the
mixture was allowed to cool to room temperature. The solvent was
removed under reduced pressure, and the blue residue was extracted
into 80 mL of pentane. The royal blue solution was cooled to -20
°C, affording very dark blue crystals with a metallic golden luster
(1.9 g, 1.97 mmol, 67% yield). The compound appears homoge-
neous and blue when crushed in a mortar. Mp (under N2 loss):
143–144 °C. The isolated crystals gave a negative AgNO3 test. 1H
NMR (C6D6, 21 °C): δ 2.65 (ν1/2 ) 170 Hz). IR (Nujol mull; CsI
windows, cm-1): 3080(vw), 1460(s), 1380(s), 1320(w), 1248(s),
1200(m), 1090(s), 923(s), 840(br vs), 810(m), 752(m), 725(w),
690(m), 638(m), 620(sh), 498(w), 485(w), 435(w), 390(m), 378(m),
360(w), 330(w), 268(m). UV–vis (methylcyclohexane, 25 °C): 614
nm (ꢀ ) 2500 Lmol · cm-1). Anal. Calcd for C44H84N2Si8Ti2: C,
54.96; H, 8.81; N, 2.91. Found: C, 54.67; H, 8.61; N, 2.62. The
compound has been prepared by another method.17
Cp′2Ti(CO)2. Cp′2Ti (1.0 g, 2.5 mmol) was dissolved in hexane
(50 mL) and exposed to 1 atm of carbon monoxide (CO). The
solution quickly changed from blue to red. After stirring for 5 min,
the solution was concentrated to a volume of 10 mL and cooled to
-20 °C. Dark red crystals formed (0.67 g, 59% yield). Mp: 125–127
An alternative method: High-purity Cp′2Ti may be easily obtained
by allowing crystalline Cp′2TiH2 to decompose into Cp′2Ti and H2
by gently warming a solution in hexane.
1
(Cp′2Ti)2(N2). Cp′2Ti (1.0 g, 2.5 mmol) was dissolved in hexane
(25 mL), and the solution was exposed to 1 atm of nitrogen. The
solution was cooled to -78 °C, and very dark crystals with metallic
golden luster formed (0.78 g, 75% yield). The compound appears
homogeneous and blue when crushed in a mortar. Mp (under N2
loss): 130–140 °C. The isolated crystals gave a negative AgNO3
test. 1H NMR (C6D6, 21 °C): δ 3.6 (ν1/2 ) 60 Hz). IR (Nujol mull;
CsI windows, cm-1): 1300(m), 1255(s), 1235(w), 1210(m), 1200(m),
1170(s), 1055(w), 1050(m), 1020(m), 950(m), 940(w), 855(s),
830(s), 815(m), 785(s), 740(w), 725(w), 670(m), 660(m), 590(w),
500(w), 460(w), 405(w). UV–vis (methylcyclohexane, 25 °C): 603
nm (ꢀ ) 1850 L mol · cm-1). Anal. Calcd for C26H42NTi: C, 74.98;
H, 10.16; N, 3.36. Found: C, 74.88; H, 10.19; N, 3.43. The EI
mass spectrum is consistent with Cp′2Ti.
°C. H NMR (C6D6, 21 °C): δ 1.17 (s, 36 H, C(CH3)3), 4.83 (d,
4
4
4H, JCH ) 2 Hz, ring-CH), 5.13 ppm (t, 2H, JCH ) 2 Hz, ring-
CH). IR (Nujol mull; CsI windows, cm-1): 1960s, 1880s, 1783m,
1308w, 1258s, 1206m, 1172m, 1055s, 950w, 935w, 922w, 899w,
855w, 830s, 815m, 777s, 766m, 745w, 730w, 705w, 680w, 660w,
565w, 500w, 455w, 400m, 360w, 320w. Anal. Calcd for
C28H42O2Ti: C, 73.35; H, 9.23. Found: C, 73.32; H, 9.41. The EI
mass spectrum showed a parent ion at m/e ) 458 amu. The parent
ion isotopic cluster was simulated (calcd %, obsvd %): 456 (10,
8), 457 (13, 12), 458 (100, 100), 459 (38, 36), 460 (15, 12), 461
(3, 0).
Cp′2Ti(PhCCPh). Freshly sublimed diphenylacetylene (0.84 g,
4.7 mmol) and Cp′2Ti (1.0 g, 2.34 mmol) were combined in a
Schlenk flask, and hexane was added (50 mL). The mixture
produced a dark red solution as it dissolved. Red crystals began to
nucleate before all of the diphenylacetylene had dissolved. The
solution was cooled to -20 °C, and red-orange crystals were
An alternative method: Under nitrogen, potassium amalgam was
prepared from 5 mL of mercury and potassium (1.2 g, 31 mmol).
Cp′2TiCl (2.95 g, 6.76 mmol) was dissolved in toluene (60 mL),
and the solution was added to the potassium amalgam. The mixture
was heated to reflux and stirred for 12 h. The stirring was halted,
and the mixture was allowed to cool to room temperature. The
solvent was removed under vacuum, and the blue residue was
extracted into 80 mL of pentane. The royal blue solution was cooled
to -20 °C, affording very dark blue crystals with a metallic golden
luster (1.75 g, 2.1 mmol, 62% yield).
Cp′′2TiCl. Tetrahydrofuran (150 mL) was added to a mixture
of TiCl3 · 3THF (13.0 g, 34.9 mmol) and Cp′′2Mg (15.5 g, 34.9
mmol). The solution turned dark blue immediately, and the mixture
was stirred for 12 h. The solvent was removed under reduced
pressure, and the resulting dark blue solid was extracted with 2 ×
150 mL of hexane. The combined extracts were concentrated to a
volume of 200 mL and cooled to -80 °C. Blue needles were
isolated (14.9 g, 85% yield). Mp: 153–154 °C. 1H NMR (C6D6, 21
°C): δ 2.66 (ν1/2 ) 340 Hz). IR (Nujol mull; CsI windows; cm-1):
3100(sh), 3090(s), 1940(br vw), 1880(br vw), 1830(w), 1805(w),
1760(w), 1460(vs), 1450v(s), 1425(m), 1408(s), 1392(m), 1382(m),
1
isolated (1.07 g, 75% yield). Mp: 169–170. °C. H NMR (C6D6,
4
21 °C): δ 1.12 (s, 36 H, C(CH3)3), 5.51 (d, 4H, JCH ) 2.7 Hz,
4
ring-CH), 7.99 (t, 2H, JCH ) 2.5 Hz, ring-CH), 6.89–7.11 (C6H5
resonances, overlapping, 10H). 13C NMR (C6D6, 21 °C): δ 202.4
(PhCCPh), 144.8 (C6H5), 143.5 (ring-CCMe3), 128.5 (C6H5), 127.7
(C6H5), 125.6 (C6H5), 113.3 (ring-CH), 109.2 (ring-CH), 34.4
(CMe3), 31.5 (CMe3). IR (Nujol mull; CsI windows, cm-1): 1642s,
1587s, 1300w, 1250s, 1195w, 1167m, 1065m, 1022m, 975w, 925w,
886w, 839s, 810w, 802w, 791s, 676w, 670s, 709w. 695s, 680w,
675w, 665w, 658w, 605w, 551w, 435m, 399m, 355m, 328m. Anal.
Calcd for C40H52Ti: C, 82.73; H, 9.02. Found: C, 82.91; H, 9.14.
Cp′2Ti(C2H4). Cp′2Ti (5.8 g, 13 mmol) was dissolved in hexane
(50 mL) and exposed to 1 atm of ethylene. The solution changed
color from blue to yellow in <5 min. The solution was filtered
and concentrated to a volume of 25 mL and cooled to -20 °C.
Yellow-green needles formed (2.2 g, 36% yield). Mp: 122–123 °C
1
(dec). H NMR (C6D6, 21 °C): δ 1.06 ((s), 36 H, C(CH3)3), 2.94
((s), 4H, C2H4), 4.34 (d, 4H, 3JCH ) 2.4 Hz, ring-CH), 9.26 (t, 2H,

2970 Organometallics, Vol. 27, No. 13, 2008
Walter et al.
3JCH ) 2.4 Hz, ring-CH). 13C NMR (C6D6, 21 °C): δ 142.9 (ring-
CCMe3), 119.1 (ring-CH), 108.6 (ring-CH), 97.8 (CH2CH2), 34.3
ppm (CMe3), 32.0 (CMe3). IR (Nujol mull; CsI windows, cm-1):
1289(m), 1249(s), 1231(m), 1198(m), 1180(w), 1164(m), 1098(s),
1020(m), 944(w), 933(m), 929(m), 918(w), 863(w), 850(s), 817(w),
800(s), 788(s), 725(w), 678(w), 659(s), 610(w), 488(s), 435(m),
384(m), 308(w). Anal. Calcd for C28H46Ti: C, 78.11; H, 10.77.
Found: C, 77.84; H, 10.87. The EI mass spectrum showed [M -
(C2H4)]+ as parent ion.
930(m), 858(s), 828(s), 810(m), 800(s), 729(br.s), 680(m), 620(br
s), 468(m), 428(sh), 402(m), 359(m), 295(w), 259(m). Anal. Calcd
for C52H84O2Ti: C, 74.61; H, 10.12. Found: C, 74.61; H, 10.01.
The EI mass spectrum showed a parent ion at m/e ) 837 amu. The
parent ion isotopic cluster was simulated (calcd %, obsvd %): 834
(2, 2), 835 (10, 9), 836 (29, 28), 837 (100, 100), 838 (69, 70), 839
(37, 37), 840 (14, 15), 841 (4, 3). However, the EI-MS also shows
a higher mass fragment due to [Cp4Ti4O4]+.
Cp′2TiH2. Cp′2Ti (4.28 g, 10.6 mmol) was dissolved in hexane
(50 mL) and exposed to 1 atm of hydrogen. The blue titanocene
solution turned dark red. While under the hydrogen atmosphere,
the solution was cooled slowly to -80 °C. Dark red crystals were
isolated, which were stable with respect to hydrogen loss under
vacuum. Mp: 152–154 °C (dec). 1H NMR (C7D8, -54 °C): δ 1.13
Acknowledgment. This work was supported by the
Director, Office of Science, Office of Basic Energy Sciences,
Material Sciences and Engineering Division of the U.S.
Department of Energy under Contract DE-AC02-05CH11231.
We thank Dr. Fred Hollander (at CHEXRAY, the U.C.
Berkeley X-ray diffraction facility) for assistance with the
crystallography, the German Academic Exchange Service
(DAAD) for a fellowship (M.D.W.), and Wayne W. Lukens
for discussions and assistance with the EPR studies.
4
(s, 36 H, C(CH3)3), 2.62 (2H, Ti-H), 5.10 (d, 4H, JCH ) 3 Hz,
ring-CH), 8.01 (t, 2H, 4JCH ) 3 Hz, ring-CH). IR (Nujol mull; CsI
windows, cm-1): 1640br s, 1295w, 1250s, 1231w, 1202m, 1166m,
1050m, 1024w, 925m, 847m, 821m, 806s, 762m, 722w, 683m,
665m, 464m, 398m. Anal. Calcd for C26H44Ti: C, 77.2; H, 10.96.
Found: C, 77.28; H, 11.23.
Supporting Information Available: Crystallographic data,
labeling diagrams, tables giving atomic positions, anisotropic
thermal parameters, bond distances, bond angles, torsion angels,
least-squares planes for each structure, solid state magnetism data
Cp′4Ti2(µ-O)2. A 0.45 g (1.05 mmol) portion of Cp′2Ti(C2H4)
was dissolved in ca. 100 mL of pentane, and the solution was
exposed to 1 atm of N2O. The color of the Cp′2Ti(C2H4) solution
changed immediately from yellow-green to bright red, and a red-
brown microcrystalline precipitate formed. The solvent was re-
moved under vacuum, and the red-brown powder was extracted
into 60 mL of hot toluene and allowed to cool to room temperature
and then to -20 °C, yielding the product as red microcrystals (0.4
g, 0.51 mmol, 97%). Cp′4Ti2(µ-O)2 was nearly insoluble in pentane
and only moderately soluble in toluene and did not react with
-1
(ꢀm vs T and µeff vs T plots) for Cp′2TiX (X ) Cl, Me, OH, H)
and Cp′′2TiCl, UV–vis spectra for Cp′′2TiCl and (Cp′′2Ti)2(N2), and
Hildebrand-Benesi plot for Cp′2TiH2. This material is available
free of charge via the Internet at http://pubs.acs.org. Structure factor
tables are available from the authors. Crystallographic data were
also deposited with Cambridge Crystallographic Data Centre.
Copies of the data (CCDC 662583–662585) can be obtained free
of charge via http://www.ccdc.cam.ac.uk/data_request/cif, by e-
mailing data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge
CB 1EZ, UK; fax +44 1223 336033.
1
DMAP or Cp′2Ti(C2H4). Mp: 228–229 °C (dec). H NMR (C6D6,
21 °C): δ 1.36 (s, 18H, C(CH3)3), 1.45 (s, 18H, C(CH3)3), 5.78 (d,
4
4
2H, JCH ) 1.3 Hz, ring-CH), 6.04 (d, 2H, JCH ) 2.7 Hz, ring-
CH), 6.33 (t, 1H, 4JCH ) 1.3 Hz, ring-CH), 6.53 (t, 1H, 4JCH ) 2.7
Hz, ring-CH). IR (Nujol mull; CsI windows, cm-1): 3080(w),
2654(sh), 1255(m), 1205(w), 1182(w), 1148(w), 1040(w), 1023(w),
OM7012315