Evaluation of the oxygen π-donation in permethyltitanocene silanolates and alcoholates

Article abstract of DOI:10.1021/om801209f

A series of compounds [Cp*₂Ti(III)OR] where R is ⁱPr₃Si (2), Ph₃Si (3), (ⁱBuO) ₃Si (4), (c-C₅H₉)₇Si ₈o₁₂ (5), and ^tBu (6) w

Full text of DOI:10.1021/om801209f

1748
Organometallics 2009, 28, 1748–1757
Evaluation of the Oxygen π-Donation in Permethyltitanocene
Silanolates and Alcoholates
Vojtech Varga,† Ivana C´ısaˇrova´,‡ Ro´bert Gyepes,‡ Michal Hora´cˇek,§ Jirˇ´ı Kubisˇta,§ and
Karel Mach§,*
´
Research Institute of Inorganic Chemistry, ReVolucˇn´ı 84, 400 01 Ust´ı nad Labem, Czech Republic,
Department of Inorganic Chemistry, Charles UniVersity, HlaVoVa 2030, 128 40 Prague 2, Czech Republic,
and J. HeyroVsky´ Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, V.V.i.,
DolejsˇkoVa 3, 182 23 Prague 8, Czech Republic
ReceiVed December 22, 2008
A series of compounds [Cp*2Ti(III)OR′] where R′ is iPr3Si (2), Ph3Si (3), (tBuO)3Si (4), (c-C5H9)7Si8O12
t
(5), and Bu (6) were prepared by protolysis of the titanium-methylene bond in singly tucked-in
permethyltitanocene [Cp*Ti(III)(η5:η1-C5Me4CH2)] with the respective silanols or tert-butanol. Their
electronic transitions from the ground-state molecules to their first excited states (dominantly a 1a1 f b2
transition) occur in the range 1300-1800 nm, originating from π-donation from oxygen lone pair electrons
to the Ti-O bond (as found by Andersen et al. J. Am. Chem. Soc. 1996, 118, 1719). The X-ray crystal
structures of 2-4 and 6 revealed that steric effects of substituents R′ change the geometry of the titanocene
moiety only negligibly. DFT calculations of the 1a1 f b2 transition for optimized structures of 2, 4, 6,
[Cp*2Ti(III)OH] (7), and [Cp*2Ti(III)OMe] (8) reproduced the dependence of experimental λ(1a1 f b2)
on electron donation/attraction properties of R′ and revealed that the decrease of the oxygen π-donation
is accompanied with an increase in negative natural charge on the OR′ group. The observed increase of
t
λ
exp(1a1 f b2) in the order of substituents R′, Me < Bu < H < Ph < SiiPr3 < SiPh3 ∼ Si(OtBu)3
< (c-C5H9)7Si8O12 (SIPOSS cluster), thus indicates the decrease of Ti-O π-interaction with an increased
polarity of the Ti-O bond. The DFT calculations of 7 with the naturally bent and collinear Ti-O-H
conformation showed only a small effect of bending on the oxygen π-donation.
silanolates was reviewed,3 and among early transition metal
Introduction
(Ti, Zr) POSS silanolates4 numerous representatives were
investigated as catalysts for the polymerization of olefins.5
There is still continuous interest in exploiting silica surface
hydroxyl groups for a controlled anchoring of homogeneous
catalysts to obtain highly selective catalysts, which could
approach the properties of, for example, single-site catalysts
for the polymerization of olefins.1 The situation with the
presence of two or three cooperative or isolated SiOH groups
on the silica surface has been successively modeled using
polyhedral oligomeric silsesquioxanes (POSS) containing
monosilanol, e.g., (c-C5H9)7Si8O12OH (SIPOSS), disilanol,
e.g., (c-C5H9)8Si8O11(OH)2 (DIPOSS), and trisilanol func-
tionalities, e.g., (c-C5H9)7Si7O9(OH)3 (TRIPOSS).2 The use
of POSS silanols for the preparation of numerous metal
In particular, single-site catalysts of the type Cp′Ti(OR′)R′′2/
M(C6F5)3 became the subject of intense research, where the
effect of any siloxy, aryloxy, or alkoxy ligands on the stability
of ion pair bimetallic complexes and their catalytic activity was
of main interest. An excellent study for Cp′ ) η5-1,3-
(SiMe3)2C5H3, OR′ ) (c-C5H9)7Si8O12O (SIPOSS) or Ph3SiO,
and R′′ ) CH2Ph, and M ) B concluded that (c-C5H9)7Si8O12OH
is a stronger Brønsted acid than Ph3SiOH and that the equilib-
rium (eq 1)
Cp′Ti(OR′)(CH2Ph)2 + B(C6F5)3< ) ) ) >
[Cp′Ti(OR′)(CH2Ph)]+[(CH2Ph)B(C6F5)3]- (1)
is shifted more to ion pairs for OR′ ) OSiPh3.6 A recent study
of the system for Cp′ ) η5-C5Me5 (Cp*), OR′ ) OSiiPr3, R′′ )
Me, and M ) B or Al proved that zwitterionic complexes
[Cp*Ti(OSiiPr3)(Me)]+[MeM(C6F5)3]- were formed and were
* To whom correspondence should be addressed. E-mail: mach@
jh-inst.cas.cz.
† Research Institute of Inorganic Chemistry.
‡ Charles University.
§ Academy of Sciences of the Czech Republic.
(1) (a) Chien, J. C. W. In Metallocene-Based Polyolefins; Scheirs, J.,
Kaminsky, W., Eds.; John Wiley and Sons Ltd.: Chichester, England, 2000;
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(c) Zecchina, A.; Groppo, E.; Bordiga, S. Chem.-Eur. J. 2007, 13, 2440–
2460. (d) Millot, N.; Cox, A.; Santini, C. C.; Molard, Y.; Basset, J.-M.
Chem.-Eur. J. 2002, 8, 1438–1442, and references therein.
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10.1021/om801209f CCC: $40.75
2009 American Chemical Society
Publication on Web 02/27/2009

Permethyltitanocene Silanolates and Alcoholates
Organometallics, Vol. 28, No. 6, 2009 1749
stable in solution for several days.7 The systems for Cp′ ) η5-
C5H5 (Cp), OR′ ) OC6H3Me2-2,6 or similar ligands, R′′ ) Me,
and M ) B generated zwitterionic complexes [CpTi(OR′)-
(Me)]+[MeB(C6F5)3]-; however, these were unstable in solution
even at -20 °C, decomposing in two concurrent ways while
eliminating methane and MeB(C6F5)2.8 The system for Cp′ )
Cp*, OR′ ) OSi(CH2CH2SiMePh2)3, R′′ ) Me, and M ) B
also generated the zwitterionic [Cp*Ti(OR′)(Me)]+-
[MeB(C6F5)3]- complex, which decomposed at room temper-
ature with t1/2 ≈ 48 h to give two decomposition products, the
same as in the preceding case.9 Apparently, the lowest stability
for complexes of this type was noticed for the expected
[Cp*Ti(OtBu)(Me)]+[MeB(C6F5)3]- complex, which decom-
posed immediately after mixing its precursors.10 The complete
elimination of isobutene however indicated a different decom-
position pathway.11
The methyl carbon atom was σ-bonded to boron, and two
hydrogen atoms of the methyl group exerted an agostic
interaction14 with the titanium atom, similarly to known
zirconocene zwitterionic complexes.15
The extent of the stabilizing effect of the OR′ group in
Cp′Ti(OR’)R′′2/M(C6F5)3 systems has been discussed in terms
of Brønsted acidity of corresponding POSS silanols16 or a pair
of SIPOSS and Ph3SiOH,6 different silylation rates of POSS
silanols,2c and reactivities of silanols, phenols, or alcohols in
protolysis reactions, e.g., with [Zr(CH2Ph)4],5a [Cp′Ti(CH2-
Ph)3],5b or [Cp*TaMe4],17a or exchange reactions, e.g.,
(tBuO)3SiOH with Ta(OiPr)5,17b or Ph3SiOH with [Ti(OtBu)4],17c
which were based mostly on a qualitative observation.
In this contribution we compare the ability of silanolate
groups (c-C5H9)7Si8O12O (SIPOSS), (tBuO)3SiO, Ph3SiO, and
t
iPr3SiO and BuO, MeO, PhO, and OH groups to act in
π-donation of a lone electron pair from oxygen to the Ti-O
bond. Bis(pentamethylcyclopentadienyl)titanium(III) oxy deriva-
tives are used as model compounds with a uniform structure of
the titanocene moiety for determination of energy of the 1a1 f b2
transition in their electronic absorption spectra, which is the
inherent measure of the effect.18 Crystal structures and density
functional theory (DFT) calculations of the model compounds
support the applicability of the method.
Generally, in the absence of the OR′ ligand, the [Cp*TiMe3]/
[B(C6F5)3] system formed a highly active catalyst for either
polymerization of ethene to a high-molecular polymer or styrene
to syndiotactic polystyrene when its components were mixed
in the presence of monomer using nonpolar solvents.12a When
no monomers were added, the reaction led to the formation of
the anticipated zwitterionic complex [Cp*TiMe2]+[MeB-
(C6F5)3]- in an NMR tube experiment at low temperature;
however, this product rapidly decomposed at room temperature
and was then inactive toward olefins.12b Replacement of one or
two Me groups with alkoxy groups led to a decrease in catalytic
activity, which was attributed to the decreased electrophilicity
of the metal resulting from π-electron donation of the alkoxy
oxygen lone pair to the empty d orbital on the metal.12c The
application of the C6F5 or OC6F5 ligands as poor π-electron
donor OR′ moieties yielded thermally unstable zwitterionic
complexes with B(C6F5)3.12d Thus, the only monocyclopenta-
dienyltitanium complexes of this type characterized by crystal-
lography are the catalytically inactive zwitterionic complexes
Results and Discussion
i
Compounds [Cp*2TiOR′] where R′ is Pr3Si (2), Ph3Si (3),
t
(tBuO)3Si (4), (c-C5H9)7Si8O12 (5), and Bu (6) were prepared
by silanolysis or alcoholysis of the titanium-methylene bond
in singly tucked-in permethyltitanocene [Cp*Ti(III)(η5:η1-
C5Me4CH2)] (1)19 with the respective silanols or tert-butanol
in a practically quantitative reaction (Scheme 1).
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[Cp*Ti(OR′)2]+[MeB(C6F5)3]-, where R′ ) Bu or Pr, the
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1750 Organometallics, Vol. 28, No. 6, 2009
Varga et al.
Scheme 1
This synthetic method was used by Pattiasina for obtaining
619b and by Edelmann et al.4d to prepare a SIPOSS compound
similar to 5. All compounds except 5 were characterized by
single-crystal X-ray diffraction analysis and EI-MS, and all
compounds by IR, UV-near IR, and EPR spectra. The EI-MS
spectra displayed abundant molecular ions for all compounds,
and their fragmentation was consistent with their molecular
structures. The fragment ions arising from elimination of Cp*
were base peaks for 2 and 3, whereas for 6, the [M - R′OH]+
ion was the base peak and the next most abundant ion was [M
- Cp*]+. The molecular ion of 4 successively eliminated butene
molecules and Cp*, giving a base peak of the composition
[Cp*TiOSi(OH)3]+. Thus the titanocene siloxides 2-4 upon
ionization preferred the loss of the Cp* ligand compared to the
alkoxide 6 with overwhelming dissociation of the alcohol. In
the infrared spectra, only the most intense absorption bands were
tentatively assigned. The valence Si-O(Ti) vibration was
assigned to the band at 897 cm-1 for 2, 956 cm-1 for 3, 1025
cm-1 for 4,20a and 1038 cm-1 for 5. The skeletal Si-O-Si
vibrations in 5 at 1117 cm-1 did not differ from that in SIPOSS,
and in 4, the bands at 1047 and 964 cm-1 were attributed to
ν(Si-O(C)) and ν(C-O(Si)) vibration, respectively. The band
at 985 cm-1 for 6 is the valence C-O vibration coupled with
ν(Ti-O),20b and the typical absorption bands for tert-butyl
Figure 1. Qualitative MO diagram for a bent titanocene after
Andersen et al.18 showing the generation of one σ, two π, and one
singly occupied nonbonding orbital.
with the electron pair in the pz orbital of X. The 1a1 f b2
transition has been observed at λ < 2000 nm for X ) F, NH2,
NHMe, OMe, OPh,18 OH,21a and [(η5-C5HMe4)2Ti(III)-
(OtBu)].21b The wavelengths of the 1a1 f b2 transition for
compounds 2-6 and literature data for similar compounds
[Cp*2Ti(III)OH] (7),21a [Cp*2Ti(III)OMe] (8), and [Cp*2Ti-
(III)OPh] (9)18 are given in Table 1. These spectroscopic data
will be correlated with the X-ray structure data for 2-4, 6, and
7 and computed optimized structure data and the 1a1 f b2
transition thereof for 2, 4, and 6-8 (see below).
Crystal Structures of 2-4 and 6. All the compounds studied
with the exception of 5 afforded suitable single crystals for X-ray
diffraction analysis. Data collection for these studies was carried
out on the same instrument within two months, minimizing thus
any data collection differences. The geometric parameters
common to all compounds are listed in Table 2, and the
PLATON drawings of compounds 2-4 and 6 are shown in
Figures 2-5.
The data prove that geometry of the titanocene moiety is very
similar for all the compounds, differing by a maximum of 3.1°
in the Cg(1)-Ti-Cg(2) angle. The sum of this angle with the
Cg(1)-Ti-O and Cg(2)-Ti-O ones makes 360° within esd’s,
confirming thus a trigonal-planar coordination environment
around the titanium atom. The value of the Cg(1)-Ti-Cg(2)
angle indicates a degree of steric congestion on the open side
of the permethyltitanocene shell caused by bulkiness of the OR′
ligand; the smaller the ligand, the larger the angle contained.
Surprisingly, the largest value of Cg(1)-Ti-Cg(2) in Table 2
indicates the smallest steric congestion for 3, which is similar
to that in [Cp*2Ti(III)CH2CMe3], showing an angle of
139.4(3)°.22 Listings of intramolecular nonbonding contacts
between the OR′ ligands and permethylcyclopentadienyl ligands
revealed that the most pronounced repulsions are those between
the oxygen atom O(Ti) and the cyclopentadienyl ring carbon
atoms C(1), C(2), C(11), and C(12), as all the compounds had
three contact distances O · · · C shorter than the sum of covalent
radii (3.22 Å) by 0.36-0.20 Å. However, the hydroxyl
groups in 4 and 6 should be those at 1192 and 1182 cm-1
,
respectively. The EPR spectra form typically a very narrow
single line (∆H ∼2.4-2.8 G) in the range g ) 1.971-1.978
flanked by about 20-times less intense multiplets due to 49Ti
(IN ) 7/2) and 47Ti (IN ) 5/2) with aTi ) 8.2-8.8 G. The
electronic absorption spectra of 2-6 displayed three well-
observable bands in the regions 497-525, 605-665, and
1300-1800 nm. Among these, the absorption band of the lowest
energy transition can indicate the presence and the extent of
π-donation ability of oxygen to the Ti-O bond.
According to the qualitative MO diagram developed by
Andersen et al.18 (Figure 1) for [(η5-C5Me5)2Ti(III)X] d1
complexes, where X was an element with a lone electron pair
in the p orbital, the transition from the SOMO orbital, essentially
2
dz perpendicular to the Cg-Ti-Cg (Cg is the centroid of gravity
of the cyclopentadienyl ring) plane, to the empty orbital dxz
becomes observable when the latter is destabilized by interaction

Permethyltitanocene Silanolates and Alcoholates
Organometallics, Vol. 28, No. 6, 2009 1751
Table 1. Experimental First Excitation (Dominantly 1a1f b2 Transition) Wavelengths (nm) for 2-9 and Calculated First Excitation
Wavelengths, Natural Charges on the Cp2*Ti Moiety, Sum of r and ꢀ Delocalization Energies O(pz)fTi (kcal/mol), Optimized O-Z (Z ) C, Si,
or H) Distances (Å), and Optimized Ti-O-Z Angles (deg) for 2, 4, and 6-8
5
4
3
2
6
7
8
9
λ
exp(1a1 f b2)
calc(1a1 f b2)
1800
1700
1451
1725
1585
1219
1300
1069
1477a
1282b
1528b
λ
1253(1224)c
0.470
1087(1081)c
0.467
qnatural Cp2*Ti
Edeloc(O(pz)fTi)
d(Ti-O)
0.607
24.96
1.953
1.629
175.36
0.570
25.22
1.930
1.669
171.14
0.452
32.65
1.876
1.421
177.17
31.68
1.893
0.967
121.96
34.45
1.853
1.392
166.51
d(O-Z)
Ti-O-Z
a Taken from ref 21a. b Taken from ref 18. c Data in parentheses are for the collinear arrangement of Ti-O-H or Ti-O-C.
Table 2. Selected Bond Lengths and Bond Angles for 2-4, 6, and 7a
4
3
2 (mol. 1)
2 (mol. 2)
6
7
Bond Lengths (Å)
2.092(2)
Ti-Cg(1)b
Ti-Cg(2)b
Ti-Pl(1)b
Ti-Pl(2)b
Ti-O
2.0867(7)
2.0878(7)
2.0863(2)
2.0873(2)
1.9244(9)
1.6032(9)
2.0928(10)
2.0850(9)
2.0917(3)
2.0848(3)
1.9190(13)
1.6115(13)
2.106(2)
2.101(2)
2.1049(7)
2.0980(7)
1.924(3)
1.637(3)
2.1137(6)
2.1179(7)
2.1136(2)
2.1164(2)
1.8658(9)
1.4137(15)c
2.070(1)
2.068(1)
2.107(2)
2.0911(7)
2.1061(7)
1.919(3)
1.889(2)
Si-O(Ti)
1.638(3)
Bond Angles (deg)
136.34(8)
Cg(1)-Ti-Cg(2)
Cg(1)-Ti-O
Cg(2)-Ti-O
Ti-O-Si
138.30(3)
111.08(4)
110.59(4)
176.89(6)
39.28(6)
139.16(4)
111.69(5)
109.10(5)
173.50(8)
38.47(9)
135.84(8)
111.22(10)
112.93(10)
174.99(18)
41.00(12)
136.04(3)
111.09(4)
112.86(4)
174.34(9)d
41.24(5)
143.79(5)
109.84(9)
106.36(9)
110.12(10)
113.54(10)
172.48(17)
40.33(12)
ꢀe
35.06(12)
a Taken from ref 21a. b Cg(1) and Cg(2) are centroids and Pl(1) and Pl(2) least-squares planes of the C(1-5) and C(11-15) cyclopentadienyl rings,
respectively. c Distance O-C(21). d Angle Ti-O-C(21). e Dihedral angle between the least-squares planes of cyclopentadienyl rings.
Figure 2. PLATON45 drawing of 2 at the 30% probability level
with atom-labeling scheme. Hydrogen atoms are omitted for clarity.
Figure 3. PLATON45 drawing of 3 at the 30% probability level
compound [Cp*2Ti(III)OH] (7), whose parameters are included
with atom-labeling scheme. Hydrogen atoms are omitted for clarity.
for comparison in Table 2, showed a larger Cg(1)-Ti-Cg(2)
angle (143.79(5)°),21a which indicates that the presence of R′
groups decreases the Cg(1)-Ti-Cg(2) angle. The methyl carbon
atoms on the cyclopentadienyl ligands are in general deviated
from the least-squares plane of the ring away from titanium,
most remarkably on the closed shell side, for the methyls in
hinge position close to the Cg(1), Ti, Cg(2) plane. The maximum
deviation was in the range 0.42-0.44 Å for all compounds
except 3, where the maximum deviation of 0.370(4) Å was
found for C(18). This steric congestion on both sides of the
titanocene shell results in only negligible tilting of the cyclo-
pentadienyl rings (see the slightly smaller Ti-Pl (Pl is the least-
squares plane of Cp* ring) distances compared to Ti-Cg ones
in Table 2). The Ti-O bond length in 6 was markedly shorter
and the average Ti-Cg distance slightly longer than in the siloxy
compounds, where these parameters differed rather negligibly.
The effect of siloxy substituents was discernible on the Si-O(Ti)
bond, which was shortened in the order 2 > 3 > 4 (Table 2).
The Ti-O-Si and Ti-O-C bond systems undergo only some
slight bending, with angles at the oxygen atom spanning from
172.48(17)° for molecule 1 of 2 to 176.89(6)° for 4 (Table 2).
The angle magnitude is apparently controlled by intramolecular
packing demands; for example, in [Cp2Ti(Cl)OSiPh3] the
Ti-O-Si angle was 164.5(2)°.23a The linear Ti-O-Si arrange-
ment was found in tripodal complexes (-O-)3TiOSiR3 with
(-O-)3 being a TRIPOSS ligand and R ) Me20a,23b or a
titanatrane with R ) Ph.23c Also the structure of [Ti(OSiPh3)4]
falls into this group of compounds with three equally bent
tripodal ligands (148.2(3)°) and a linear one. It is of interest
that the Ti-O bond of the latter is longer (1.798(7) Å) and the
Si-O bond shorter (1.613(7) Å) than the bonds in the three
equal bent ligands (Ti-O 1.782(4) Å and Si-O 1.650(4) Å).17c
The Ti-O-C bond system apparently prefers a bent arrange-
ment. In [(η5-C5HMe4)2Ti(III)(OtBu)], where the Cg(1)-Ti-Cg(2)
angle 136.7(1)° is close to that of 6 because one cyclopenta-
dienyl ring is oriented with its proton-bearing carbon atom to a

1752 Organometallics, Vol. 28, No. 6, 2009
Varga et al.
Figure 4. PLATON45 drawing of 4 at the 30% probability level
with atom-labeling scheme. Hydrogen atoms are omitted for clarity.
Figure 6. Optimized geometric parameters for 8: Ti-Cg av 2.10
Å, Ti-O 1.853 Å, C-O 1.392 Å, Cg-Ti-Cg 141.78, and
Ti-O-C angle 166.51°.
differed systematically from crystallographic ones showing
slightly longer Ti-O, Si-O, and C-O bonds and similar
Ti-O-Si or Ti-O-C angles (cf. Tables 1 and 2). The
systematic elongation of the above bonds resulted presumably
from a larger steric congestion in the optimized molecules that
was caused by a notable elongation of all C-H bonds due to
the temperature dependence of ideal hydrogen positions to cope
with libration in the solid state.
The optimized structure 8 (Figure 6) showed slightly shorter
Ti-O and O-C bond lengths compared to those of optimized
6, while the Ti-O-C angle was coplanar with the Cg-Ti-Cg
angle plane and was smaller compared to that of optimized 6.
The computed 1a1 f b2 transitions for all the optimized
structures showed a systematic shift to shorter wavelengths by
200-250 nm from the experimental values; however, the effect
of substituents R′ on band positions could be reproduced within
both series. Compared with the hydroxyl hydrogen in compound
7, the electron-donating methyl and tert-butyl substituents in 8
and 6 shifted the experimental as well as computed 1a1 f b2
transition to shorter wavelengths, whereas the opposite effect
was unequivocally established for the computed 1a1 f b2
transition of siloxy compounds 2 and 4 and experimental spectra
of 2-5 and 9 (see Table 1). The discrepancy between
experimental and calculated transition energies could be caused
by numerical difficulties arising from the treatment of systems
with a low HOMO-LUMO separation; more advanced multi-
configurational methods however could not be employed due
to the prohibitive size of the complexes under study.
The generally known electron-donating/attracting effects of
substituents R′ primarily influence polarity of the Ti-O bond.
The ionic nature of the Cp*2Ti(III)OR′ compounds is visualized
for 7 by distribution of electrostatic potential (Figure 7), and
the Ti-O bond polarity is reflected in natural charges on the
Cp*2Ti moiety (Table 1). These values, ranging from 0.452 for
6 to 0.607 for 4, would reach the limit of 1.0 for the free ion
Cp*2Ti+. Provided the structure of the Cp*2Ti moiety is virtually
constant, the same negative charges have to be induced on the
OR′ counterpart of the complexes. The absolute values of natural
charges in Table 1 thus reflect the effect of R′ on the Ti-O
bond polarity. The largest ionic contribution to the Ti-O bond
is found for 4, and an even higher ionic contribution is to be
expected for 5 with the yet more polarized Ti-O-Si(OSi(R)O)3
moiety.
Figure 5. PLATON45 drawing of 6 at the 30% probability level
with atom-labeling scheme. Hydrogen atoms are omitted for clarity.
hinge position and the other to the OtBu group, the Ti-O-C
angle (162.16(13)°) is smaller than in 6, utilizing the space of
the missing methyl group.21b In a number of alkoxy and aryloxy
Ti(IV) complexes [Cp2TiCl(OR)] (R ) aryl)24a and [(η5-
C5H4SiMe3)2TiCl(OR)] (R ) CH2-ferrocenyl or aryl)24b and in
sterically nonhindered [Cp2TiCl(OEt)]24c the Ti-O-C angles
were in the range 130-150°. The extremely small Ti-O-H
angle of 112(4)° found for 721a was optimized to 121.9° by
DFT structure optimization (see below), close to the crystal-
lographic values for [Cp*2Ti(OH)2],25a [Cp*2Ti(OH)(CCPh],25b
and [Cp*2Ti(OH)(H2O)]+[BPh4]-.25c In 4, where the Si-O-C
bond systems are not sterically hindered, their average bending
was 137.02(9)°, average Si-O bond length 1.6307(10) Å, and
average O-C bond length 1.4415(17) Å. The closely related
compound 5, whose crystal structure could not be determined,
apparently would fall into the above-outlined trend of keeping
a constant Ti-O bond length and shortening of the Si-O(Ti)
bond length since the similar compound [Cp*2TiOR′] with R′
being (cyclohexyl)7Si7O9(OSiMe3)2 (TriPOSS with two trim-
ethylsilylated hydroxyl groups) exerted a Ti-O bond length of
1.927(2) Å and Si-O(Ti) of 1.595(2) Å.4d
DFT Calculations. The structures of compounds 2, 4, and
6-8 were optimized using the crystallographic parameters as
input data except for 8, where the crystallographic data for 6
were modified by replacing the tert-butyl group with a methyl
group. The optimized geometric parameters for 2, 4, 6, and 7

Permethyltitanocene Silanolates and Alcoholates
Organometallics, Vol. 28, No. 6, 2009 1753
Figure 7. Isodensity surface (2%) color-coded with the electrostatic potential (left) and orientation of the molecule 7 within the isodensity
surface (center), and molecule 7 (right). Color values for the electrostatic potential: blue >0.10, light blue 0.05, green 0.00, yellow -0.05,
red <-0.20.
Figure 8. Correlation diagram for 7 with the collinear (left) and bent (right) Ti-O-H conformation.
A quantitative evaluation of covalent contributions was carried
out by means of natural bond analysis. Due to the prevalence
of the electrostatic attraction between the bent Cp*2Ti moiety
and the O-R groups, the default NBO search reported only lone
pairs on the oxygen atoms. At the second-order donor-acceptor
perturbation level the delocalization energies from the oxygen
pz lone pair to the non-Lewis metallic lone pairs followed the
changes of the first excitation energies. The acceptor orbital for
the oxygen pz is the dxy orbital on the metal, resulting in a neat
π-interaction. The delocalization energies O(pz)fTi follow the
reverse trend of natural charges (Table 1), in agreement with
the anticipated assumption that the more polar the Ti-O bond,
the weaker the covalent interaction. A direct comparison of the
σ-contributions to the Ti-O bonding would be inappropriate,
due to the entirely different genesis of the Si-O bond in
comparison with the “regular” C-O and H-O σ-bonds. The
third-row silicon atom achieves its bonding through the forma-
tion of σ* orbitals. In this type of bonding, the inductive effects
play a nonanticipated important role.26
Figure 9. The σ- (left) and the π-coordination in 7. Both molecular
orbitals are doubly occupied. Orbital contours are plotted at the
5% probability level.
present case. For both conformations the SOMO 1a1 orbital of
2
the complex is a nearly pure dz , incapable of providing a good
overlap with any of the ligand orbitals, and the LUMO b2 arises
from interaction of the lone electron pair in the pz oxygen orbital,
which overlaps with the empty dxz orbital of titanium, as found
by Andersen et al.18 (Figure 1). For the bent conformation, the
corresponding bonding orbital is HOMO and the π-bonding
character of the Ti-O bond is well observable in Figure 9. In
distinction to a correlation diagram in Figure 1, the σ-bond
To understand the nature and extent of the covalent contribu-
tion to the Ti-O bonding, an interaction diagram was devised
for the simplest compound, 7, in its optimized bent (121.96°)
and collinear Ti-O-H conformation using Counterpoise DFT27
(Figure 8).
2
2
This type of calculation allows the examination of frontier
orbitals not only for the real complex itself but also for its
constituting fragments, chosen to be Cp*2Ti+ and OH- in the
represented by the next lower orbital arises from the dx -y orbital
overlapping with the other electron lone pair of oxygen, which
is close in energy (Figure 9, left). The oxygen sp orbital binding

1754 Organometallics, Vol. 28, No. 6, 2009
Varga et al.
For the actually studied compounds with the solid-state
Ti-O-C angle of >170° the λexp(1a1 f b2) values are pertinent
rather to a collinear conformation due to the solution averaging;
however, the above investigation of bent and collinear confor-
mations of 7 and 8 proved that the difference in λexp(1a1 f b2)
and λcalc(1a1 f b2) cannot account for the different bending in
solution and in the solid state. A low sensitivity of λexp(1a1 f
b2) to the Ti-O-C angle was recently confirmed by observation
that the tethered alkoxy compounds 10 and 11 from Chart 1,
which both have Ti-O-C angles of 133°, displayed absorption
bands at 1365 and 1500 nm, respectively.29 It is highly probable
that the red shift in 11 with respect to 10 is caused by the
presence of the aryl substituent; however, it is not clear whether
the red shift of only 65 nm for 10 with respect to 6 (1300 nm)
is caused by the smaller Ti-O-C angle or by other factors,
e.g., the remote attachment of its carbon atom to an aromatic
cyclopentadienyl ring.
Figure 10. Ti-O π-bonding in the collinear 7 arising from
interaction of dxy and py orbitals (left) and dxz and pz orbitals (right).
Both molecular orbitals are doubly occupied. Orbital contours are
plotted at the 5% probability level.
the hydroxyl group lies too low in energy to provide an effective
2
2
interaction with the dx -y orbital (Supporting Information,
extended correlation diagram, listing of relevant orbitals and
MO energies).
Conclusions
The first electronic absorption band of [Cp*2Ti(III)OR′]
compounds 2-9 in the near-infrared region is suitable for
detection of the oxygen π-donation effect and evaluation of its
extent. The absorption band was assigned to the 1a1 f b2
transition, whose energy was proportional to the magnitude of
the oxygen π-donation.18 The X-ray diffraction analysis of
compounds 2-4 and 6 revealed that steric effects of substituents
R′ change the geometry of the titanocene moiety only negligibly,
and hence, the oxygen π-donation effect is controlled by the
electron donation/attraction effect of substituent R′ via a
decrease/increase of the Ti-O bond polarity. According to
A collinear Ti-O-H arrangement rotates the orbital orienta-
tion on the oxygen atom directing the O-H sp hybrid orbital
exactly toward the metallic center (Figure 8, left). Although
this hybrid orbital has in principle a proper shape for mixing
2
2
with the metal dx -y orbital, their actual overlap is prevented
by the large energy separation of the fragment orbitals. The
only remaining possible interaction for the oxygen lone electron
pair in the py orbital is with the dxy orbital. Thus a weak π-bond
is formed that is orthogonal to the other π-bond, which is now
lower in energy (Figure 10). This formation of a π orbital instead
of a σ one results in weakening of the Ti-O bond. It is
evidenced by the decrease of the calculated Ti-O Mayer bond
order from 1.1 for the bent conformation to 0.6 for the collinear
one, while the Mayer bond order for the O-H bond remains
unchanged (0.8). As concerns the λcalc(1a1 f b2), the conforma-
tion of the Ti-O-H angle has only a small effect (see Table
1) since the overlap of pz and dxz orbitals is affected negligibly
by the angle change. A total energy difference for the bent and
collinear 7 was found to be only 6.60 kcal/mol.
λ
exp(1a1 f b2) for 2-9, occurring in the range 1280-1800 nm,
the oxygen π-donation decreased in the order of substituents
Me > Bu > H > Ph > SiiPr3 > SiPh3 ∼ Si(OtBu)3
>
t
(c-C5H9)7Si8O12 (SIPOSS cluster). The same order of substituent
effects was obtained for λcalc(1a1 f b2) calculated by DFT
methods for optimized structures 2, 4, and 6-8. Calculated natural
charges for the Cp*2Ti moiety (equal to negative charges on OR′)
increased following the order of increasing λcalc(1a1 f b2), whereas
the calculated delocalization energies O(pz)fTi displayed a
reverse trend. This is in agreement with the anticipated
assumption that the more polar the Ti-O bond, the weaker
the covalent interaction. Calculations on compound 7 with the
natural bent and collinear Ti-O-H moiety revealed that the
oxygen π-donation depends only slightly on the bending angle.
This was corroborated for the Ti-O-C case by analogous
treatment of optimized bent and collinear Ti-O-C in 8. The
obtained order of substituent effects should be of general validity
for evaluation of oxygen π-donation in titanocene Ti(IV)
complexes as well as in half-sandwich titanocene complexes
for catalytic application in olefin polymerization. Experiments
on titanocene alkoxy-tethered compounds with a Ti-O-C angle
of about 130° (Chart 1) and DFT calculations of oxygen
π-donation in these compounds are under way.
Although not accessible experimentally, the generally reiter-
ated statement that the oxygen π-donation effect should be
enhanced with the linear conformation of the Ti-O-C system24,28
was investigated in detail by DFT computations for compound
8. The optimized molecule of 8 with the Ti-O-C angle of
166.5° and with the linear one yielded a Mayer bond order of
1.3 for the bent conformer and 1.2 for the collinear one and a
λcalc(1a1 f b2) of 1087 and 1081 nm, respectively (Table 1).
These values indicate that a linear arrangement only slightly
enhances the lone pair π-donation effect, in agreement with the
results for 7.
(24) (a) Besancon, J.; Top, S.; Tirouflet, J.; Dusausoy, Y.; Lecomte,
C.; Protas, J. J. Organomet. Chem. 1977, 127, 153–168. (b) Ko¨cher, S.;
Walfort, B.; Rheinwald, G.; Ru¨ffer, T.; Lang, H. J. Organomet. Chem. 2008,
693, 3213–3222. (c) Huffman, J. C.; Moloy, K. G.; Marsella, J. A.; Caulton,
K. G. J. Am. Chem. Soc. 1980, 102, 3009–3014.
Experimental Section
(25) (a) Pellny, P.-M.; Burlakov, V. V.; Baumann, W.; Spannenberg,
A.; Rosenthal, U. Z. Anorg. Allg. Chem. 1999, 625, 910–918. (b) Polse,
J. L.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 5393–
5394. (c) Bochmann, M.; Jaggar, A. J.; Wilson, L. M.; Hursthouse, M. B.;
Motevalli, M. Polyhedron 1989, 8, 1838–1843.
(26) Ploom, A.; Tuulmets, A. J. Organomet. Chem. 2009, 694, 313–
315.
General Considerations. Reactions of 1 with dehydrated and
degassed alcohols were carried out under vacuum on a vacuum
line in sealed all-glass devices equipped with breakable seals or
under an argon atmosphere. EI-MS spectra were measured on a
VG-7070E mass spectrometer at 70 eV. Crystalline samples in
(27) Simon, S.; Duran, M.; Dannenberg, J. J. J. Chem. Phys. 1996, 105,
11024–11031.
(28) Stroot, J.; Beckhaus, R.; Saak, W.; Haase, D.; Lu¨tzen, A. Eur.
J. Inorg. Chem. 2002, 1729–1737, and references therein.
(29) Varga, V.; C´ısarˇova´, I.; Hora´cˇek, M.; Pinkas, J.; Kubisˇta, J.; Mach,
K. Collect. Czech. Chem. Commun. 2009, 74, DOI: 10.1135/cccc2008212.

Permethyltitanocene Silanolates and Alcoholates
Organometallics, Vol. 28, No. 6, 2009 1755
Chart 1
(10). IR (KBr, cm-1): 2946 (s), 2908 (s), 2863 (s), 2720 (vw), 1494
(w), 1467 (m), 1450 (m), 1379 (m), 1246 (w), 1064 (vw), 1022
(w), 1011 (w), 996 (vw), 978 (vw), 897 (vs), 805 (vw), 666 (m),
633 (w), 563 (vw), 438 (m). EPR (hexane, 22 °C): g ) 1.974, ∆H
) 2.8 G, a(Ti) ) 8.8 G. EPR (toluene, -140 °C): g1 ) 2.000, g2
) 1.980, g3 ) 1.949, gav ) 1.976. UV-near IR (hexane, nm): 505
> 650 ∼ 1585. Anal. Calcd for C29H51OSiTi (491.68): C, 70.84;
H, 10.45. Found: C, 70.80; H, 10.41.
Data for 3 are as follows. Yield of green crystals was 0.73 g
(78%). Mp: 220 °C. EI-MS (200 °C): m/z (relative abundance) 596
(9), 595 (16), 594 (28), 593 (M+•; 46), 592 (12), 591 (10), 461
(10), 460 (24), 459 (46), 458 ([M - Cp*]+; 100), 457 (26), 456
(18), 317 ([M - HOR′]+; 13), 276 ([M - Cp* - SiPh2]+; 10),
259 ([SiPh3]+; 10), 258 (10), 202 (10), 201 (11), 200 (16), 199
([M - Cp* - SiPh3]+; 16), 181 (11), 168 (11), 135 (26), 119 (23),
105 (17), 91 (16). IR (KBr, cm-1): 3066 (w), 3047 (vw), 3009 (vw),
2995 (w), 2974 (vw), 2904 (m), 2857 (w), 2720 (vw), 1589 (vw),
1484 (w), 1451 (w), 1428 (m), 1379 (w), 1256 (vw), 1189 (vw),
1109 (s), 1030 (vw), 1002 (w), 956 (vs), 804 (vw), 744 (w), 703
(s), 514 (s), 502 (m), 420 (m). EPR (toluene, 22 °C): g ) 1.973,
∆H ) 2.4 G. aTi ) 8.4 G. EPR (toluene, -140 °C): g1 ) 2.000, g2
) 1.982, g3 ) 1.941, gav ) 1.974. UV-near IR (toluene, nm): 500
> 642 ∼ 1725. Anal. Calcd for C38H45OSiTi (593.73): C, 76.87;
H, 7.64. Found: C, 76.91; H, 7.66.
sealed capillaries were opened and inserted into the direct inlet under
argon. The spectra are represented by the peaks of relative
abundance higher than 7% and by important peaks of lower
intensity. Crystals for EI-MS measurements and melting point
determinations were placed in glass capillaries, and KBr pellets
for IR spectra were pressed in a Labmaster 130 (mBraun) glovebox
under purified nitrogen (concentrations of oxygen and water were
lower than 2.0 ppm) and sealed with flame. IR spectra were
measured in an air-protecting cuvette on a Nicolet Avatar FT IR
spectrometer in the range 400-4000 cm-1. X-Band EPR spectra
were recorded on an ERS-220 spectrometer (Center for Production
of Scientific Instruments, Academy of Sciences of GDR, Berlin,
Germany) operated by a CU-3 unit (Magnettech, Berlin, Germany).
g-Values were determined by using an Mn2+ standard at g ) 1.9860
(MI ) -1/2 line). A STT-3 variable-temperature unit was used for
measurements in the range -140 to +25 °C. UV-near IR spectra
in the range 300-2000 nm were measured on a Varian Cary 17D
spectrometer in all-sealed quartz cells (Hellma).
Chemicals. The solvents, hexane and toluene were dried by
refluxing over LiAlH4 and stored as solutions of green dimeric
titanocene [(µ-η5:η5-C5H4C5H4)(µ-H)2{Ti(η5-C5H5)}2].30 The single
tucked-in permethyltitanocene, [Ti(III){η5:η1-C5Me4(CH2)}(η5-
C5Me5)] (1), was prepared from [TiCl2(η5-C5Me5)2] via [TiCl(η5-
C5Me5)2], and [TiMe(η5-C5Me5)2] by thermolysis of the latter at
110 °C for 3 h.19c Commercial silanols tris(tert-butoxy)silanol,
(Me3CO)3SiOH, triisopropylsilanol, (Me2HC)3SiOH, triphenylsil-
anol, (C6H5)3SiOH, and [3,5,7,9,11,13,15-heptacyclopentyl-
pentacyclo[9.5.1.13,9.15,15.17,13]octasiloxan-1-ol, (c-C5H9)7Si7O12-
SiOH (SIPOSS) (all Aldrich) were degassed and used as such.
tert-Butanol (Aldrich) was dehydrated by treating with doubly
tucked-in permethyltitanocene followed by vacuum distillation.31
Preparation of Permethytitanocene Silanolates. Compound 1
(0.50 g, 1.57 mmol) was dissolved in hexane (20 mL), and the
solution mixed with a solution of the respective silanol (1.60 mmol)
in hexane. The initial intense purple color of 1 turned nearly
immediately to a pale pink color of the product. After stirring for
20 min the volume of the solution was reduced by vacuum
distillation to make a nearly saturated solution. This was cooled to
-5 or -28 °C for crystallization. The crystals were separated from
the mother liquor and recrystallized from hexane. Yields were not
optimized, well-defined crystals were collected for X-ray diffraction
analysis, and the same material was used for EI-MS, IR, UV-near
IR, and EPR characterization.
Data for 4 are as follows. Yield of brownish-green crystals was
0.78 g (86%). Mp: 130 °C with decomposition. EI-MS (110 °C):
m/z (relative abundance) 583 (17), 582 (35), 581 (M+•; 69), 580
(11), 508 ([M - OBu]+; 11), 446 ([M - Cp*]+; 5), 390 ([M -
Cp* - C4H8]+; 7) 389 (6), 374 ([M - OBu - C5Me4CH2]+; 10),
335 (9), 334 ([M - Cp* - 2C4H8]+; 15), 333 (12), 319 (6), 318
(19), 317 ([M - HOR′]+; 23), 280 (21), 279 (43), 278 ([M - Cp*
-3C4H8]+; 100), 277 (64), 276 (22), 262 (27), 261 (24), 260 ([M
- Cp* - 3C4H8 - H2O]+; 30), 259 (19), 249 (23), 198
([(C5Me4CH2)TiO]+; 17), 137 (33), 135 (25), 134 (20), 133 (10),
119 (20), 105 (10), 79 (24), 57 (94). IR (KBr, cm-1): 2974 (s),
2927 (m), 2903 (m), 2867 (m), 2722 (vw), 1495 (vw), 1472 (w),
1444 (w), 1388 (m), 1362 (m), 1236 (m), 1215 (m), 1192 (s), 1047
(vs), 1025 (s), 964 (vs), 819 (w), 684 (m), 620 (vw), 526 (w), 495
(m), 474 (w), 438 (m), 423 (m). EPR (toluene, 22 °C): g ) 1.972,
∆H ) 2.6 G, aTi ) 8.3 G. EPR (toluene, -140 °C): g1 ) 1.999, g2
) 1.981, g3 ) 1.939, gav ) 1.973. UV-near IR (hexane, nm): 318
(sh) > 374 (sh) > 497 > 665 ∼ 1700. Anal. Calcd for C32H57O4SiTi
(581.76): C, 66.07; H, 9.88. Found: C, 65.98; H, 9.83.
Preparation of 5. Compound 1 (0.30 g, 0.94 mmol) was
dissolved in hexane (20 mL), and the solution mixed with a solution
of SIPOSS (0.86 g, 0.94 mmol) in hexane (10 mL). The initial
intense purple color of 1 turned nearly immediately to a pale pink
color of the product. After stirring for 30 min the volume of the
reaction solution was reduced to ca. 5 mL by evaporation of hexane
under vacuum, and the solution was cooled to -28 °C overnight.
A pale purple crystalline solid was separated from the mother liquor
and dissolved in hexane and in toluene for spectroscopic measure-
ments. Attempts to prepare single crystals suitable for X-ray
diffraction analysis failed; the crystals lost solvent of crystallization
both under vacuum and in a nitrogen atmosphere.
Data for 2 are as follows. Yield of green crystals was 0.55 g
(72%). Mp: 180-185 °C. EI-MS (110 °C): m/z (relative abundance)
493 (10), 492 (17), 491 (M+•; 38), 448 ([M - Pr]+; 15), 358 (18),
357 (33), 356 ([M - Cp*]+; 100), 355 (15), 354 (15), 353 (14),
318 (17), 317 ([M - HOR′]+; 13), 316 (11), 315 (16), 314 ([M -
Cp* - C3H6]+; 47), 272 ([M - Cp* - 2C3H6]+; 21), 228 (11),
227 (10), 226 (10), 225 (10), 224 (13), 181 (13), 134 (10), 119
Data for 5 are as follows. IR (KBr, cm-1): 2950 (s), 2912 (w),
2866 (m), 2720 (vw), 1493 (vw), 1453 (w), 1382 (w), 1248 (w),
1117 (vs), 1038 (s), 948 (vw), 916 (w), 727 (vw), 617 (vw), 579
(vw), 509 (m), 422 (w). EPR (toluene, 22 °C): g ) 1.9714, ∆H )
2.7 G, aTi ) 8.2 G. EPR (toluene, -140 °C): g1 ) 2.000, g2 )
1.983, g3 ) 1.934, gav ) 1.972. UV-near IR (hexane, nm): 504 >
605(sh) ∼ 1800.
Preparation of 6. Compound 1 (0.50 g, 1.57 mmol) was
dissolved in hexane (20 mL), and t-BuOH (0.2 mL, 2.10 mmol)
was added. The initial intense purple color of 1 became immediately
less intense. The reaction solution was evaporated under vacuum
to remove hexane with excess t-BuOH, and a purple residue was
(30) Antropiusova´, H.; Dosedlova´, A.; Hanusˇ, V.; Mach, K. Transition
Met. Chem. (London) 1981, 6, 90–93.
ˇ
(31) Pinkas, J.; Gyepes, R.; C´ısaˇrova´, I.; Hora´cˇek, M.; Steˇpnicˇka, P.;
Kubisˇta, J.; Varga, V.; Mach, K. Collect. Czech. Chem. Commun. 2008,
73, 967–982.

1756 Organometallics, Vol. 28, No. 6, 2009
Varga et al.
Table 3. Crystallographic Data and Data Collection and Structure Refinement Details for 2-4 and 6
4
3
2
6
formula
mol wt
cryst syst
space group
a (Å)
b (Å)
c (Å)
R (deg)
ꢁ (deg)
γ (deg)
V (Å3)
C32H57O4SiTi
581.77
C38H45OSiTi
593.73
C29H51OSiTi
491.69
C24H39OTi
391.45
triclinic
orthorhombic
Pbca (No. 61)
20.6532(2)
14.3925(2)
22.6067(3)
90
triclinic
monoclinic
P21/c (No. 14)
14.89220(10)
10.8752(2)
14.7644(2)
90
109.4532(9)
90
2254.67(5)
4
j
j
P1 (No. 2)
P1 (No. 2)
10.5233(2)
11.1081(2)
15.3903(3)
83.5103(11)
87.7159(11)
69.6085(10)
1675.49(5)
2
1.153
0.323
brown-green
0.5 × 0.4 × 0.3
150(2)
11.8550(3)
14.9147(4)
16.2430(4)
92.0898(13)
90.2051(16)
94.6256(16)
2860.67(13)
4
90
90
6719.87(14)
8
1.174
0.318
green
Z
Dcalcd (g cm-3
)
1.142
0.359
green
1.153
0.389
purple
µ (mm-1
)
color
cryst size (mm3)
0.5 × 0.4 × 0.2
0.5 × 0.25 × 0.16
0.5 × 0.4 × 0.36
T (K)
150(2)
150(2)
150(2)
θ
min; θmax (deg)
1.33; 27.57
-13/13
1.95; 27.48
-26/26
-18/18
-29/29
84 166
1.82; 25.10
-14/14
2.93; 27.51
-19/19
range of h
range of k
range of l
no. of rflns collected
no. of unique reflns
F(000)
-14/14
-17/17
-14/14
-19/19
36 181
7713
634
-0/19
40 988
10 062
1076
-19/19
49 598
5179
852
7704
2536
no. of params refined
R(F); wR(F2) all data (%)
GooF (F2), all data
R(F); wR(F2) (I > 2σ(I)) (%)
362
4.07; 9.01
1.026
3.37; 8.52
0.291; -0.473
380
6.59; 11.68
1.035
4.22; 10.26
0.367; -0.321
611
7.84; 16.84
1.121
6.54; 16.00
0.867; -0.451
248
3.58; 9.02
1.040
3.20; 8.73
0.311; -0.258
∆F (e Å-3
)
dissolved in 5 mL of hexane. The solution was cooled to -28 °C
for 2 days, and a mass of purple crystals was separated from the
mother liquor. The crystals were recrystallized from a minimum
of hexane to give small needle crystals for X-ray diffraction analysis
and spectroscopic characterization. The mother liquor after a partial
evaporation of hexane afforded another crop of purple crystals that
gave the same spectral data as the recrystallized ones. Total yield:
0.50 g (82%).
Data for 6 are as follows. Mp: 122 °C. EI-MS (80 °C): m/z
(relative abundance) 393 (16), 392 (41), 391 (M+•; 95), 390 (17),
389 (15), 336 (23), 335 ([M - C4H8]+; 84), 334 (20), 319 (26),
318 (75), 317 ([M - HOR′]+; 100), 316 (30), 315 (26), 257 (16),
256 ([M - Cp*]+; 64), 255 (31), 241 (21), 240 ([M - Cp* -
CH4]+; 90), 239 (28), 201 (20), 200 (89), 199 (45), 198 (33), 196
(13), 195 (30), 183 (23), 182 (90), 181 (48), 180 (54), 179 (19),
178 (34), 177 (17), 119 (13). IR (KBr, cm-1): 3002 (m,sh), 2964
(s), 2906 (vs), 2862 (m), 2720 (vw), 1499 (w), 1439 (m,b), 1378
(s), 1351 (m), 1208 (m), 1182 (vs), 1062 (vw), 1022 (m), 985 (vs),
803 (vw), 775 (m), 528 (m), 482 (vw), 462 (w). EPR (hexane, 22
°C): g ) 1.978, ∆H ) 2.7 G, aTi ) 8.5 G. EPR (toluene, -140
°C): g1 ) 2.000, g2 ) 1.980, g3 ) 1.957, gav ) 1.979. UV-near IR
(hexane, nm): 525 > ∼650 (sh) > ∼1300. Anal. Calcd for C24H39OTi
(391.44): C, 73.64; H, 10.04. Found: C, 73.56; H, 10.00. The IR
and EPR data agree with those reported.32
the optimization procedure. Numerical integration was done on a
pruned grid having 99 radial shells each of 590 angular points.
Natural bonding analysis36 was carried out by the NBO 3.1 program
integrated in Gaussian.37 Mayer bond order38 determination and
natural bonding analysis were carried out employing only the
6-31+G(d,p) basis set on the optimized geometries of 2, 4, and
6-8. The electronic transitions were computed by time-dependent
DFT39 using the relativistic effective potential of Hurley et al.40
for Ti, the potential of Pacios and Christiansen41 for Si (if
applicable), and the 6-31++G(d,p) basis set for all other atoms
against the same geometries as the bond order analyses. Visualiza-
tion and examination of molecular orbitals was accomplished by
Molden.42
X-ray Crystallography. Single crystals or crystal fragments of
2-5 were mounted on Lindemann glass capillaries in a Labmaster
130 glovebox (mBraun) under purified nitrogen. Diffraction data
for all complexes were collected on a Nonius KappaCCD diffrac-
tometer (Mo KR radiation, λ ) 0.71073 Å) and processed by the
HKL program package.43 The phase problem was solved by direct
methods (SIR97),44 followed by consecutive Fourier syntheses, and
refined by full-matrix least-squares on F2 (SHELXL-97).45 Relevant
(36) Carpenter, J. E.; Weinhold, F. J. Mol. Struct. (THEOCHEM) 1988,
169, 41–62.
(37) Glendening, E. D.; Badenhoop, J. K.; Reed, A. E.; Carpenter, J. E.;
Weinhold, F. NBO Version 3.1; Theoretical Chemistry Institute, University
of Wisconsin: Madison, WI.
(38) Bridgemann, A. J.; Cavigliasso, G.; Ireland, L. R.; Rothery, J.
J. Chem. Soc., Dalton Trans. 2001, 2095–2108.
(39) Stratmann, R. E.; Scuseria, G. E.; Frisch, M. J. J. Chem. Phys.
1998, 109, 8218–8224.
(40) Hurley, M. M.; Pacios, L. F.; Christiansen, P. A.; Ross, R. B.;
Ermler, W. C. J. Chem. Phys. 1986, 84, 6840–6853.
(41) Pacios, L. F.; Christiansen, P. A. J. Chem. Phys. 1985, 82, 2664–
2671.
Computational Details. DFT studies have been carried out at
the Fermi cluster at the J. Heyrovsky´ Institute of Physical Chemistry,
Academy of Sciences of Czech Republic, v.v.i., using Gaussian
03, revision E.01.33 All calculations used the Becke exchange34
and the Perdew/Wang 91 correlational functionals.35 The geometries
of 2, 4, and 6 were optimized using the 6-311G(3d,p) basis set and
those of 7 and 8 using the 6-311G(d,p) basis set employed for all
atoms and an analytical Hessian computed before the first step of
(42) 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.
(43) Otwinowski, Z.; Minor, W. HKL Denzo and Scalepack program
package by Nonius. Methods Enzymol. 1997, 276, 307–326.
(44) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Polidori, G. J. Appl. Crystallogr. 1994, 27, 435–
436.
(32) Pattiasina, J. W.; Heeres, H. J.; van Bolhuis, F.; Meetsma, A.;
Teuben, J. H.; Spek, A. L. Organometallics 1987, 6, 1004–1010.
(33) Frisch, M. J.; et al. Gaussian 03, ReVision E.01; Gaussian, Inc.:
Wallingford, CT, 2004.
(34) Becke, A. D. Phys. ReV. A 1988, 38, 3098–3100.
(35) Perdew, J. P.; Burke, K.; Wang, Y. Phys. ReV. 1996, B54, 16533–
16539.

Permethyltitanocene Silanolates and Alcoholates
Organometallics, Vol. 28, No. 6, 2009 1757
crystallographic data are given in Table 3. All non-hydrogen atoms
were refined anisotropically. Hydrogen atoms were included in
idealized positions and refined isotropically using the riding model.
Molecular graphics was carried out with the PLATON program.46
and PLATON drawing at 30% probability for structures 2, 3, 4,
and 6, correlation diagram for bent 7, R orbital energies for 7,
molecular orbitals from correlation diagram, and the full ref 33.
This material is available free of charge via the Internet at
http://pubs.acs.org.
Acknowledgment. This research was supported by the
Academy of Sciences of the Czech Republic (Grant No.
KAN100400701) and the Ministry of Education, Youth and
Sports (Project No. LC06070), I.C. and R.G. are grateful to
MSM0021620857.
OM801209F
(45) Sheldrick, G. M. SHELXL97, Program for Crystal Structure
Refinement from Diffraction Data; University of Go¨ttingen: Go¨ttingen, 1997.
(46) Spek, A. L. PLATON, A Multipurpose Crystallographic Tool;
Utrecht University: Utrecht, The Netherlands, 2007.
Supporting Information Available: CIF file for structures 2,
3, 4, and 6. UV-near IR spectra of 2-6, supporting information