Facile synthesis and X-ray structures of (η5-C5Me5)Ti(OArF)3 (OArF = OC6F5, OCH2C6F5, and OCH2C6F2H3)

Article abstract of DOI:10.1016/j.jorganchem.2007.05.008

New half-sandwich titanocene complexes (η⁵-C₅Me₅)Ti(OC₆F₅)₃ (1), (η⁵-C₅Me₅)Ti(OCH₂C₆F₅)₃ (2), and (η⁵-C₅Me₅)Ti(OCH₂C₆F₂H₃)₃ (3) were synthesized via the displacement of methoxide ligands in (η⁵-C₅Me₅)Ti(OMe)₃ by the corresponding aryloxy or benzyloxy ligands. These compounds have been fully characterized by various spectroscopic methods including X-ray crystallography. Compound 1 has a distorted three-legged piano stool structure. However, complexes 2 and 3 have the chariot-like structure, where chariot means a two-wheeled horse-drawn vehicle. The π electron donation of oxygen atom to Ti center in complexes 1-3 is considerable.

Full text of DOI:10.1016/j.jorganchem.2007.05.008

Journal of Organometallic Chemistry 692 (2007) 3593–3598
www.elsevier.com/locate/jorganchem
Note
Facile synthesis and X-ray structures of (g5-C5Me5)Ti(OArF)3
(OArF = OC6F5, OCH2C6F5, and OCH2C6F2H3)
a
a,
b,
*
Junseong Lee , Youngkyu Do *, Youngjo Kim
a
Department of Chemistry, School of Molecular Science BK21, Center for Molecular Design and Synthesis, KAIST, Daejeon 305-701, Republic of Korea
b
Department of Chemistry, Chungbuk National University, Cheongju, Chungbuk 361-763, Republic of Korea
Received 28 March 2007; received in revised form 26 April 2007; accepted 1 May 2007
Available online 10 May 2007
Abstract
New half-sandwich titanocene complexes (g5-C5Me5)Ti(OC6F5)3 (1), (g5-C5Me5)Ti(OCH2C6F5)3 (2), and (g5-C5Me5)Ti(OCH2C6-
F2H3)3 (3) were synthesized via the displacement of methoxide ligands in (g5-C5Me5)Ti(OMe)3 by the corresponding aryloxy or
benzyloxy ligands. These compounds have been fully characterized by various spectroscopic methods including X-ray crystallogra-
phy. Compound 1 has a distorted three-legged piano stool structure. However, complexes 2 and 3 have the chariot-like structure,
where chariot means a two-wheeled horse-drawn vehicle. The p electron donation of oxygen atom to Ti center in complexes 1–3 is
considerable.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Titanium; Half-sandwich metallocene; X-ray structure; Pentafluorophenol; Pentafluorobenzylalcohol; 2,5-Difluorobenzylalcohol; Penta-
methylcyclopentadienyl; p–p Interaction
1. Introduction
Bu, and so on) [5,6]. Several types of (g5-C5Me5)Ti(OR0)3
have been synthesized by a two-step reaction in which LiOR0
is made from R0OH and n-BuLi, followed by reaction with a
third equivalent of (g5-C5Me5)TiCl3 [5,6]. However, yields
were somewhat low and some by-product could be obtained.
Other synthetic route to (g5-C5Me5)Ti(OR0)3 is an amine or
methane displacement with alkoxide ligand using (g5-
C5Me5)TiMe3 or ðg5-C5Me5ÞTiðNR02Þ3 [7], which is com-
mercially unavailable and difficult to purify. In addition,
complexes of the type (g5-C5Me5)Ti(OR0)3 complexes can
be prepared by reacting Cp0TiCl3 with R0OH in the presence
of NEt3 [8] in spite of the high dependence of yield on R0
group. In this regard, we are interested in the facile one-pot
and quantitative synthetic route to (g5-C5Me5)Ti(OR0)3
using commercially available starting materials. Herein
we report the simple one-pot and quantitative synthesis,
characterization, and X-ray structures of complexes (g5-
C5Me5)Ti(OC6F5)3 (1), (g5-C5Me5)Ti(OCH2C6F5)3 (2),
and (g5- C5Me5)Ti(OCH2C6F2H3)3 (3) from the reaction
between commercially available (g5-C5Me5)Ti(OMe)3 and
corresponding aryloxy or benzyloxy ligand.
Since the discovery of the Ziegler–Natta catalyst systems
in early 1950s [1], tremendous advances in the design and
application of organometallic complexes as a-olefin poly-
merization catalysts have been achieved [2]. Of the extensive
previous work, most has focused on the development of cat-
alytic systems based on cyclopentadienyl group 4 com-
pounds suitable for the polymerization of monomers such
as ethylene, propylene, and styrene. However, there are only
few reports for the polymerization catalysis using non-
bridged Cp0TiX3 complexes, which contain both one pen-
tahapto ligand and three monodentate ligands, though
the syntheses of these complexes have been known for
several decades [3]. The examples include (g5-C5R5)TiCl3
[4] and (g5-C5Me5)Ti(OR0)3 (R = H and Me; R0 = Me, Et,
*
Corresponding authors. Tel./fax: +82 42 869 2829 (Y. Do), Tel.: +82
43 261 3395; fax: +82 43 267 2279 (Y. Kim).
E-mail addresses: ykdo@kaist.ac.kr (Y. Do), ykim@cbu.ac.kr (Y. Kim).
0022-328X/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.05.008

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J. Lee et al. / Journal of Organometallic Chemistry 692 (2007) 3593–3598
2. Experimental
2.1. General procedures
2.4. Synthesis of (g5- C5Me5)Ti(OCH2C6F2H3)3 (3)
The desired product 3 as yellow crystals was prepared in
an isolated yield of 96% (1.18 g) in a manner analogous to
the procedure for 1 using 2,5-difluorobenzylalcohol(0.89 g,
6.2 mmol) and (g5-C5Me5)Ti(OMe)3 (0.55 g, 2 mmol).
1H NMR (CDCl3, 300.133 MHz): d = 7.1–6.6 (m, 9H,
OCH2C6F2H3), 5.25(s, 6H, OCH2C6F2H3), 2.02 (s, 15H,
C5 Me5).
All reactions were carried out under dinitrogen atmo-
sphere using standard Schlenk and glove box techniques
[9]. Dinitrogen was deoxygenated with activated Cu cata-
lyst and dried with drierite. All chemicals were purchased
from Aldrich and were used as supplied unless otherwise
indicated. Cp*Ti(OMe)3 were purchased from Strem Co.
All solvents (Aldrich anhydrous grade) were dried by dis-
tilling from sodium–potassium alloy (n-hexane) or CaH2
(dichloromethane) under a dinitrogen atmosphere and
stored over the activated molecular sieves 3A [10]. CDCl3
was dried over activated molecular sieves (4A) and were
used after vacuum transfer to a Schlenk tube equipped with
19F NMR (CDCl3, 282.376 MHz): d = ꢀ119.73 (d, 3H,
J = 18.4 Hz), ꢀ126.74 (d, 3H, J = 18.4 Hz).
Anal. Calc. for C31H30F6O3Ti: C, 60.80; H, 4.94. Found:
C, 60.80; H, 5.03%.
2.5. X-ray structural determination
1
J. Young valve. H, 13C{1H} and 19F NMR spectra were
The crystals were coated with paraton oil. The diffrac-
tion data for 1 were collected on a Bruker 1K SMART
CCD-based diffractometer with graphite-monochromated
recorded at ambient temperature on a Bruker AM300 spec-
trometer using standard parameters. The chemical shifts
are referenced to the peaks of residual CDCl3 (d 7.24 in
1H NMR). Elemental analyses were performed by EA
1110-FISONS(CE).
˚
Mo Ka radiation (k = 0.7107 A). The hemisphere of reflec-
tion data were collected as x scan frames with 0.3ꢁ/frame
and an exposure time of 5 s/frame. Cell parameters were
determined and refined by the SMART program [11]. Data
reduction were performed using SAINT software [12]. The
data were corrected for Lorentz and polarization effects.
An empirical absorption correction was applied using the
SADABS program [13]. The diffraction data of complexes 2
and 3 were measured at 193 K with synchrotron radia-
2.2. Synthesis of (g5-C5Me5)Ti(OC6F5)3 (1)
To a dichloromethane solution of (g5-C5Me5)Ti(OMe)3
(0.55 g, 2 mmol) was added dropwise at ꢀ78 ꢁC a solu-
tion of pentafluorophenol (1.14 g, 6.2 mmol) in 30 mL
of dichloromethane. The reaction mixture was warmed
to room temperature and stirred for 12 h. The residue,
obtained by removing the solvent under vacuum, was
washed with 20 ml of n-hexane several times. The desired
product 1 was isolated as orange crystals after recrystalli-
zation from the dichloromethane/n-hexane solution at
ꢀ20 ꢁC in a refrigerator for overnight (1.43 g, 98%).
1H NMR (CDCl3, 300.133 MHz): d = 2.18 (s, 15H, C5-
Me5).
˚
tion (k = 0.75000 A) on a 4AMXW ADSC Quantum-210
detector with a silicon double crystal monochromator at
the Pohang Accelerator Laboratory, Korea. The HKL2000
(Ver.0.98.689) [14] was used for data collection, cell refine-
ment, reduction, and absorption correction. The structures
of the compounds were solved by direct methods and
refined by full matrix least-squares methods using the SHEL-
XTL program package with anisotropic thermal parameters
for all non-hydrogen atoms [15]. Further details are listed
in Tables 1 and 2.
19F NMR (CDCl3, 282.376 MHz): d = ꢀ168.74 (t, 3H,
J = 22.0 Hz), ꢀ165.47 (dd, 6H, J = 21.5 and 18.6 Hz),
ꢀ160.60 (m, 6H).
3. Results and discussion
Anal. Calc. for C28H15F15O3Ti: C, 45.93; H, 2.06.
Found: C, 46.04; H, 2.20%.
Complexes 1–3 could be prepared via the displacement
of methoxide ligands in (g5-C5Me5)Ti(OMe)3 by the corre-
sponding fluorine-substituted aryloxy or benzyloxy ligands.
The treatment of commercially available (g5-C5Me5)Ti-
(OMe)3 with three equivalents of pentafluorophenol, penta-
fluorobenzylalcohol, or 2,5-difluorobenzylalcohol ligand in
dichloromethane gave, after workup, the new half-sand-
wich titanocene 1–3 as orange or yellow crystals in more
than 95% isolated yield. Unlike the previous reported liter-
ature [4–8], attempted reaction between (g5-C5Me5)TiCl3
and corresponding lithiated aryloxy or benzyloxy species
in toluene or THF was not successful and a mixture of
the desired product with non-separable impurities was
obtained. In addition, the same result was observed in the
reaction between (g5-C5Me5)TiCl3 and corresponding spe-
cies in the presence of NEt3. These suggest that the reaction
2.3. Synthesis of (g5-C5Me5)Ti(OCH2C6F5)3 (2)
The desired product 2 as yellow crystals was prepared
in an isolated yield of 95 % (1.49 g) in a manner analo-
gous to the procedure for 1 using pentafluorobenzylalco-
hol (1.23 g, 6.2 mmol) and (g5-C5Me5)Ti(OMe)3 (0.55 g,
2 mmol).
1H NMR (CDCl3, 300.133 MHz): d = 5.17 (s, 6H,
OCH2PhF5), 1.96 (s, 15H, C5Me5).
19F NMR (CDCl3, 282.376 MHz): d = ꢀ163.13 (m, 6H),
ꢀ155.95 (t, 3H, J = 20.3 Hz), ꢀ145.50 (dd, 6H, J = 13.3
and 8.75 Hz).
Anal. Calc. for C31H21F15O3Ti: C, 48.08; H, 2.73.
Found: C, 48.43; H, 2.62%.

J. Lee et al. / Journal of Organometallic Chemistry 692 (2007) 3593–3598
3595
Table 1
Crystallographic data and parameters for 1–3
Table 2
Selected bond lengths (A) and angles (ꢁ) for 1–3
˚
Compound
1
2
3
1
2
3
Empirical
formula
Formula weight 366.15
(C28H15F15O3Ti)1/2 C31H21F15O3Ti C31H30F6O3Ti
Ti–O1
Ti–O2
Ti–O3
Ti–(g5-C5Me5 centroid)
O1–C11
1.840(2)
1.848(6)
1.840(2)
2.034(3)
1.325(3)
1.324(7)
1.325(3)
1.8544(13)
1.8108(14)
1.8237(24)
2.0444(10)
1.416(2)
1.803(4)
1.860(5)
1.808(5)
2.035(4)
1.404(7)
1.422(8)
1.571(12)
774.38
612.45
Crystal system Monoclinic
Monoclinic
P21/c
12.433(3)
8.7550(18)
28.694(6)
90
94.81(3)
90
3112.4(11)
4
Triclinic
ꢀ
Space group
P21/m
8.532(3)
16.188(6)
10.283(4)
90
90.603(7)
90
1420.1(9)
4
P1
˚
a (A)
11.081(2)
11.671(2)
13.257(3)
96.32(3)
105.81(3)
117.60(3)
1404.5(5)
2
O2–C18
O3–C25
1.390(3)
1.397(3)
˚
b (A)
˚
c (A)
(g5-C5Me5 centroid)–Ti–O1
(g5-C5Me5 centroid)–Ti–O2
(g5-C5Me5 centroid)–Ti–O3
O1–Ti–O2
O1–Ti–O3
O2–Ti–O3
Ti–O1–C11
Ti–O2–C18
Ti–O3–C25
115.77(1)
118.37(1)
115.77(1)
101.69(6)
101.47(9)
101.69(6)
162.53(19)
158.55(25)
162.53(19)
109.31(6)
119.66(6)
118.42(6)
102.74(6)
102.57(6)
101.84(6)
122.51(10)
155.69(12)
145.58(12)
121.1(2)
110.9(2)
115.5(3)
101.46(21)
101.5(2)
104.3(3)
166.7(4)
119.9(4)
134.2(6)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
dcalcd (g/cm3)
F(000)
1.713
1.653
1.448
728
1552
632
Crystal size
(mm)
0.5 · 0.4 · 0.2
0.3 · 0.3 · 0.2
0.4 · 0.3 · 0.2
T (K)
193(2)
193(2)
193(2)
l(Mo Ka)
0.71073
0.75000
0.75000
(mmꢀ1
)
plexes in 2 and 3 did not show any chemical shift owing
to the existence of methylene group as a buffer between
O and electron-withdrawing phenyl group.
In order to confirm the molecular structure and to eluci-
date the metal–ligand bonding in these complexes, the
single-crystal X-ray diffraction studies for 1–3 were per-
formed. Single-crystal X-ray structure for 1–3 are shown in
Figs. 1–3, respectively. The selected bond distances and
selected bond angles are given in Table 2.
Like other half-sandwich titanocene complexes [8], com-
pound 1 has a distorted ‘‘three-legged piano stool’’ structure
as shown in Fig. 1. Compound 1 has a crystallographic mir-
ror plane embracing Ti, O2, and C18 in Fig. 1. Actually,
C11i and O1i, which stand for atoms generated by mirror
plane, in CIF file are replaced by C25 and O3 in Fig. 1,
respectively, for comparison with compounds 2 and 3. How-
ever, complex 2 and 3 have the chariot-like structure, where
chariot means a two-wheeled horse-drawn vehicle (see Figs.
2 and 3). The average Ti–O bond distances for all three oxy-
h Range (ꢁ)
Number of
unique
reflections
Number of
observed
1.98 6 h 6 27.92
1.64 6 h 6 28.67 1.66 6 h 6 20.84
8290
13210
7709
2792
2792
3245
reflections
(I > 2r(I ))
Number of
parameters
refined
278
456
457
R1(I > 2r(I ))a
0.0475
0.0475
0.1323
1.072
0.0776
0.2184
1.056
wR2(I > 2r(I ))b 0.1269
Goodness-of-fit 1.011
(I > 2r(I))
P
P
a
R1 ¼ jjF oj ꢀ jF cjj= jF oj.
P
P
2
2
1=2
b
wR2 ¼ ½ ½wðF 2o ꢀ F c2Þ ꢁ= ½wðF 2oÞ ꢁꢁ
.
˚
˚
gens in each of 1 [1.843(3) A], 2 [1.8296(17) A], and 3
condition of methoxide-elimination is essential and
required for the synthesis of 1–3.
˚
[1.824(5) A] are similar to the average of this distance
Compounds 1–3 in the solid state were slightly moisture
and air sensitive. According to 1H NMR spectroscopy,
they decomposed slightly after a few days at room temper-
ature in CDCl3 solutions contained in capped NMR tubes.
As expected, they are freely soluble in toluene, THF, and
dichloromethane. Interestingly, they are slightly soluble
even in hydrocarbon solvents such as n-hexane and n-
pentane.
The 1H and 19F NMR spectra of complexes 1–3 display
well-defined resonances with their expected integrations.
However, their 13C{1H} NMR spectra were not informa-
tive due to the complicated peaks arising from JC–F
coupling. In comparison to the starting precursor (g5-
C5Me5)Ti(OMe)3, methyl signals of g5-C5Me5 in complex
1
1 are shifted to downfield (0.17 ppm) in H NMR, which
is a consequence of the electron-withdrawing effect from
Fig. 1. X-ray structure for compound 1 and atom labeling. (H atoms were
omitted for clarity.)
OC6F5. Unusually, methyl signals of g5-C5Me5 in com-

3596
J. Lee et al. / Journal of Organometallic Chemistry 692 (2007) 3593–3598
Ti–O2–C18 = 119.96(41)ꢁ, Ti–O3–C25 = 134.23(61)ꢁ for
3]. Large Ti–O–C angles and short Ti–O distances, which
affect stability of metal center and enhancement of catalytic
behavior, would be indicative of double bond character for
the Ti–O bond due to p-electron donation from the aryloxy
or benzyloxy ligands [17].
Three phenyl rings in compound 1 are almost parallel to
g5-C5Me5 ring, where the dihedral angles between phenyl
ring and g5-C5Me5 ring are 9.1ꢁ, 6.5ꢁ, and 9.1ꢁ (see
Fig. 1). However, 2 and 3 have the totally different struc-
ture from 1. They exhibit interesting intra- and intermolec-
ular p–p stackings. Although packing effect cannot be
excluded, those probably relate to the flexibility of benzyl
group. One phenyl ring is parallel to g5-C5Me5 ring but
other phenyl rings, which have strong internal p–p interac-
tion, are perpendicular to g5-C5Me5 ring (see Figs. 2 and
3). Dihedral angles between two parallel phenyl rings are
20.78ꢁ for 2 and 11.3(10)ꢁ for 3 and their distances between
Fig. 2. X-ray structure for compound 2 and atom labeling. (H atoms were
omitted for clarity.)
˚
˚
centroids are 3.9720(16) A for 2 and 3.655(12) A for 3. In
addition, average dihedral angles between one of parallel
phenyl rings and g5-C5Me5 ring are 75.04(10)ꢁ for 2 and
86.0(9)ꢁ for 3. Furthermore, the phenyl ring unrelated to
the internal p–p interaction in complex 2 is almost parallel
to the g5-C5Me5 ring in the adjacent molecule with the
dihedral angle at 3.82(10)ꢁ and the distance between their
˚
centroids is 3.5985(14) A, which supports the existence of
external p–p interaction. Interestingly, complex 3 has inter-
nal fluorine–fluorine interaction. Even in disordered struc-
ture, this interaction is preserved. (The distances between
˚
F5 and F3 or between F5 and F3a are 3.396(16) A and
˚
3.311(18) A, respectively.) (see Fig. 4) Cone angle of ben-
zyloxy ligands was measured to estimate the steric hin-
drance around titanium center. As expected, the decrease
of cone angle in the order of 1 (72.52–72.36ꢁ) > 2 (57.31–
64.48ꢁ) > 3 (55.20–60.97ꢁ) means that steric hindrance of
phenyl ring is greater than that of benzyl group.
Fig. 3. X-ray structure for compound 3 and atom labeling. (H atoms were
In conclusion, novel half-sandwich titanocene complexes
(g5-C5Me5)Ti(OC6F5)3 (1), (g5-C5Me5)Ti(OCH2C6F5)3 (2),
and (g5- C5Me5)Ti(OCH2C6F2H3)3 (3) were synthesized via
methoxide displacement in (g5-C5Me5)Ti(OMe)3 with pen-
tafluorophenol, pentafluorobenzylalcohol or 2,5-difluorob-
enzylalcohol ligand, respectively, and characterized by X-
ray crystallography. Compounds 2 and 3 have internal p–p
interaction and also compound 2 has external p–p interac-
tion. The p electron donations of oxygen to titanium center
in these complexes are considerable. Detail studies for olefin
polymerization behaviors using 1–3 are in progress.
omitted for clarity.)
observed for titanium complexes having Ti–O bonds [8,16].
5
˚
The Ti to g -C5Me5 centroid distance [2.034(3) A for 1,
˚
˚
2.0444(10) A for 2, and 2.035(4) A for3] is in a reasonable
range [8,16]. The (g5-C5Me5 centroid)–Ti–O angles range
from 115.77(1)ꢁ to 118.37(1)ꢁ for 1, from 109.31(6)ꢁ to
119.66(6)ꢁ for 2, and from 110.9(2)ꢁ to 121.1(2)ꢁ for 3, sim-
ilar to those [from 111.14ꢁ to 118.4ꢁ] found for structurally
related compounds [8,16]. The average O–Ti–O angles in
each of 1 [101.62(7)ꢁ], 2 [102.38(6)ꢁ], and 3 [102.42(24)ꢁ]
are in the normal range [8g,16]. The bond angles among
Ti, oxygen and the ipso carbon of the aryl rings in 1 are
somewhat regular [Ti–O1–C11 = 162.53(19)ꢁ, Ti–O2–
C18 = 158.55(25)ꢁ, Ti–O3–C25 = 162.53(19)ꢁ]. However,
the bond angles among Ti, oxygen and methylene carbon
of phenyl ring in 2 and 3 fluctuate very widely [Ti–
O1–C11 = 122.51(10)ꢁ, Ti–O2–C18 = 155.69(11)ꢁ, Ti–O3–
C25 = 145.56(11)ꢁ for 2 and Ti–O1–C11 = 166.67(41)ꢁ,
4. Supplementary material
CCDC 641403, 641404 and 641405 contain the supple-
mentary crystallographic data for 1, 2 and 3. These data
can be obtained free of charge via http://www.ccdc.cam.a-
c.uk/conts/retrieving.html, or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK, fax: (+44) 1223-336-033, or e-mail: deposit@-
ccdc.cam.ac.uk.

J. Lee et al. / Journal of Organometallic Chemistry 692 (2007) 3593–3598
3597
Fig. 4. X-ray structure for disordered pair of compound 3. (H atoms were omitted for clarity.)
(b) F. Zhu, Y. Fang, H. Chen, S. Lin, Macromolecules 33 (2000)
5006.
Acknowledgements
[7] (a) A. Snell, G. Kehr, O. Kataeva, R. Fro¨hlich, G. Erker, J.
Organometal. Chem. 687 (2003) 171;
Y.K. acknowledges the Korea Research Foundation
Grant Funded by the Korean Government (MOEHRD,
Basic Research Promotion Fund) (KRF-2005-003-
C00099) for supporting this research. Y.D. is grateful for
financial support from CMDS (KOSEF) and the BK-21
project. The authors acknowledge PAL for beam line use
(Grant 2006-3041-10).
´
´
(b) P. Gomez-Sal, B. Royo, P. Royo, R. Serrano, I. SaEz, S.
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