Non-bridged amido cyclopentadienyl complexes of titanium: Synthesis, characterization, and olefin polymerization catalysis

Article abstract of DOI:10.1016/S0022-328X(99)00701-9

Alkylation of Ti(η⁵-C₅Me₅)(NMe₂)Cl₂ gives thermally stable, crystalline dialkyl complexes Ti(η⁵-C₅Me₅)(NMe₂)R₂ (R=Me, CH₂Ph, Ph). The molecular structure of the dibenzyl complex reveals an unprecedented conformation of the doubly bonded NMe₂ group which is turned parallel to the η⁵-C₅Me₅ ligand, according to single-crystal X-ray diffraction studies. Treatment of the dibenzyl complex with B(C₆F₅)₃ in d⁵-bromobenzene solution results in the quantitative formation of a thermally (>10°C) unstable monobenzyl cation as solvent-separated ion pair [Ti(η⁵-C₅Me₅)(NMe₂)CH ₂Ph]⁺ [PhCH₂B(C₆F₅)₃]^- which efficiently polymerizes styrene syndiospecifically at 25°C. Ethylene is polymerized by Ti(η⁵-C₅Me₅)(NMe₂)Cl ₂-methylalumoxane with low activity.

Full text of DOI:10.1016/S0022-328X(99)00701-9

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Journal of Organometallic Chemistry 598 (2000) 179–181
Non-bridged amido cyclopentadienyl complexes of titanium:
synthesis, characterization, and olefin polymerization catalysis
Piet-Jan Sinnema, Thomas P. Spaniol, Jun Okuda *
Institut fu¨r Anorganische Chemie und Analytische Chemie, Johannes Gutenberg-Uni6ersita¨t, Duesberg-Weg 10–14, D-55099 Mainz, Germany
Received 13 September 1999; accepted 12 November 1999
Abstract
Alkylation of Ti(h5-C5Me5)(NMe2)Cl2 gives thermally stable, crystalline dialkyl complexes Ti(h5-C5Me5)(NMe2)R2 (R=Me,
CH2Ph, Ph). The molecular structure of the dibenzyl complex reveals an unprecedented conformation of the doubly bonded NMe2
group which is turned parallel to the h5-C5Me5 ligand, according to single-crystal X-ray diffraction studies. Treatment of the
dibenzyl complex with B(C6F5)3 in d5-bromobenzene solution results in the quantitative formation of a thermally (\10°C)
unstable monobenzyl cation as solvent-separated ion pair [Ti(h5-C5Me5)(NMe2)CH2Ph]+ [PhCH2B(C6F5)3]− which efficiently
polymerizes styrene syndiospecifically at 25°C. Ethylene is polymerized by Ti(h5-C5Me5)(NMe2)Cl2ꢀmethylalumoxane with low
activity. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Titanium; Amido ligand; Half-sandwich complex; Benzyl cation; Styrene polymerization
monomer [5c]. We report here the synthesis and charac-
terization of titanium amido half-sandwich complexes
that lack any linking group between the cyclopentadi-
enyl ligand and the amido function.
1. Introduction
Titanium complexes featuring a linked amido-cy-
clopentadienyl ligand Ti(h5:h1-C5R%ZNR%%)X2 [1] are
4
considered to be the first non- or post-metallocene [2]
catalysts for the homogeneous olefin polymerization by
providing electrophilic 12-electron alkyl cations of the
2. Results and discussion
type [Ti(h5:h1-C5R%ZNR%%)R]+ [3]. Whereas the varia-
4
When Ti(h5-C5Me5)Cl3 is reacted with one equivalent
of LiNMe2 in ethereal solution, the mono(amido) com-
plex Ti(h5-C5Me5)(NMe2)Cl2 can be isolated in 75%
yield as dark red crystals [8]. In agreement with the
presence of a doubly-bonded (s+pp–dp) amido ligand
with low barrier to rotation [9], only one temperature
tion of the substituents on the amido and cyclopentadi-
enyl moieties R% and R%% has been studied extensively in
the recent past, the nature of the bridge Z was kept thus
far, fairly constant (SiMe2 [4], CH2CH2 [5,6b,c],
CH2CH2CH2 [5]). A short link such as SiMe2 between
the two ancillary ligands is assumed to be necessary for
the polymerization catalysis to perform well [6]. This
may be ascribed to the generation of a sterically more
open reaction site by virtue of the chelate effect [7]. It
has also become evident that only a specific combina-
tion of R%, R%% and Z leads to an enhanced activity,
since the ligand sphere critically influences the cation–
anion interaction and thus the accessibility of the
1
invariant signal is observed for the NMe2 group by H-
and 13C-NMR spectroscopy (l 3.01 and 43.7, respec-
tively). Reaction of the dichloro complex with the
alkylating reagents LiMe, Mg(CH2Ph)2(Et2O)2, and
LiPh gives the corresponding dialkyl complexes Ti(h5-
C5Me5)(NMe2)R2 (R=Me, CH2Ph, Ph) in good yields
as yellow (R=Me, Ph) or red (R=CH2Ph) crystals.
The dibenzyl complex shows 1H- and 13C-NMR
spectroscopic features similar to those of Ti(h5-
C5Me5)(CH2Ph)3 [10], Ti(h5-C5Me4SiMe2NR)(CH2Ph)2
[11] or Ti(h5-C5Me4CH2C6H4O)(CH2Ph)2 [12]. Thus the
* Corresponding author. Tel.: +49-6131-3923737; fax: +49-6131-
3925605.
E-mail address: okuda@mail.uni-mainz.de (J. Okuda)
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00701-9

180
P.-J. Sinnema et al. / Journal of Organometallic Chemistry 598 (2000) 179–181
1
benzyl resonance at l 92.2 with JCH=146 Hz in the
13C-NMR spectrum. This ion pair decomposes above
0°C to give a mixture of yet unidentified products. The
dimethyl complex also reacts analogously with B(C6F5)3
to give the ion pair [Ti(h5-C5Me5)(NMe2)Me]+ [MeB-
(C6F5)3]− which, however, is engaged in a dissociative
equilibrium with the starting materials.
resonances for the benzyl AB protons appear at l 1.87
and 2.24 (2JAB=10.8 Hz) and the carbon resonance
is recorded at l 81.5 with 1JCH=125 Hz. The
single-crystal X-ray structure analysis revealed a typical
three-legged piano-stool configuration (Fig. 1) with one
of the two benzyl groups showing a slight distortion, as
judged by the increased angle at C13 of 120.9(2)°. Most
notably, the NMe2 ligand is not oriented perpendicular
to the C5Me5 ring [9] as all other mono(amido)
complexes of the type Ti(h5-C5R%)(NR%%)X2. Rather the
plane containing the planar amido–nitrogen atom
forms an angle of 26° with that of the C5Me5 ring.
Given the low rotational barrier of the NMe2 group,
this feature is not surprising, but not encountered so far
in related complexes. The competition between the
amido ligand and one of the two benzyl groups for the
empty d-orbital probably induces this distortion [9].
Reaction of the dibenzyl complex with B(C6F5)3 in
d5-bromobenzene at −30°C results in the clean
formation of the dark brown mono(benzyl) cation as
a solvent-separated ion pair [Ti(h5-C5Me5)(NMe2)-
(CH2Ph)]+ [PhCH2B(C6F5)3]− (Scheme 1). Character-
istic NMR spectroscopic features for this assignment
include the value for Dl(p,m-F) of 2.9 ppm [13] and the
Styrene is efficiently polymerized by a solution
containing [Ti(h5-C5Me5)(NMe2)R]+ [RB(C6F5)3]− in
toluene at 25°C to give highly syndiotactic polymer
with Tm=273°C. Under the same conditions, the
linked amido–cyclopentadienyl derivative [Ti(h5-C5-
Me4SiMe2NMe)(CH2Ph)]+ [PhCH2B(C6F5)3]− is virt-
ually inactive [14]. The methylalumoxane-activated
dichloro complex Ti(h5-C5Me5)(NMe2)Cl2 polymerizes
ethylene only sluggishly (70 g polymer mol−1 Ti·h·bar;
toluene, 50°C, Ti:Al=2000). These results clearly
indicate the critical role of the covalent link between the
amido and the cyclopentadienyl ligand in half-sandwich
titanium catalysts [15]: the presence of the chelate
ligand suppresses the formation of Ti(III) species
responsible for the syndiospecific styrene polymer-
ization [16], at the same time stabilizing the Ti(IV) alkyl
cation for ethylene polymerization.
5
2
3. Experimental
3.1. Synthesis of Ti(p5-C5Me5)(NMe2)(CH2Ph)2
To a cooled (−78°C) mixture of 1.55 g (5.20 mmol)
of Ti(h5-C5Me5)(NMe2)Cl2 and 1.84 g (5.19 mmol) of
Mg(CH2Ph)2(Et2O)2, 40 ml of ether was added slowly.
The mixture was stirred and warmed to room tempera-
ture within 3 h while the solution turned dark red.
After an additional stirring for 30 min at room temper-
ature, the ether was removed in vacuum leaving a dark
red residue. The residue was stripped with 25 ml of
pentane and extracted with 50 ml of pentane. Concen-
tration of the dark red solution to 10 ml and slow
cooling to −30°C afforded red crystals; yield: 1.43 g
(3.49 mmol, 67%). 1H-NMR (400.1 MHz, C6D6): l 7.20
Fig. 1. ORTEP diagram of the molecular structure of Ti(h5-
3
3
C5Me5)(NMe2)(CH2Ph)2. Thermal ellipsoids are drawn at a 50%
(t, JHH=7.6 Hz, 4H, meta-C6H5), 6.92 (t, JHH=7.4
3
,
probability level. Selected bond lengths (A) and angles (°): TiꢀN,
Hz, 2H, para-C6H5), 6.88 (d, JHH=7.2 Hz, 4H, ortho-
1.887(2); TiꢀC13, 2.159(2); Tiꢀ20, 2.162(3); TiꢀCp(centroid), 2.079(2);
Cp(centroid)ꢀTiꢀN, 122.2(1); C13ꢀTiꢀC20, 100.9(1); TiꢀC13ꢀC14,
120.9(2); TiꢀC20ꢀC21, 114.0(2).
2
C6H5), 2.56 (s, 6H, NMe2), 2.24 (d, JAB=10.8 Hz, 2H,
2
CH2Ph), 1.87 (d, JAB=10.8 Hz, 2H, CH2Ph), 1.71 (s,
15H, C5Me5). 13C-NMR (100.6 MHz, C6D6): l 152.16
(s, ipso-C6H5), 128.16 (d, 1JCH=154.3 Hz, ortho-C6H5),
126.61 (d, 1JCH=154.6 Hz, meta-C6H5), 121.80 (d,
1JCH=158.0 Hz, para-C6H5), 120.72 (s, C5Me5), 81.48
(t, 1JCH=124.8 Hz, CH2Ph), 43.69 (q, 1JCH=134.2 Hz,
1
NMe2), 11.27 (q, JCH=126.4 Hz, C5Me5). Anal. Calc.
for C26H35NTi: C, 76.27; H, 8.62; N, 3.42. Found: C,
75.65; H, 8.39; N, 4.39%. Crystal data: C26H35NTi,
Mr=409.45, crystal size 1.10×0.48×0.22 mm, V=
3
1164.5(2) A , Dcalc. 1.168 Mg m−3, triclinic, P1, a=
,
(
Scheme 1.

P.-J. Sinnema et al. / Journal of Organometallic Chemistry 598 (2000) 179–181
181
,
8.0974(7), b=9.9735(6), c=14.648(1) A, h=94.114(5),
schen Industrie and the European Community (TMR
programme).
i=99.131(7), k=90.877(6)°, Z=2, F(000)=440, 7219
reflections collected in 05h511, −145k514,
−205l520 measured in the q range of 3–30°, 6777
[Rint=0.0158] independent reflections, 5132 observed
reflections, 359 parameters, final R indices [I\2|(I)]:
R1=0.0554, wR2=0.1338, R indices (all data): R1=
0.0850, wR2=0.1673, goodness-of-fit on F2 1.109,
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−3
,
A
.
3.2. Reaction of Ti(p5-C5Me5)(NMe2)(CH2Ph)2 with
B(C6F5)3
Precooled (−30°C) solutions of Ti(h5-C5Me5)-
(NMe2)(CH2Ph)2 (27 mg, 66 mmol) and B(C6F5)3 (34 mg,
66 mmol) in 0.3 ml of C6D5Br were each mixed in the cold
to give a dark yellow–brown solution. The combined
solution was transferred quickly to a precooled NMR
tube and the spectra were recorded at various tempera-
1
tures. H-NMR (400.1 MHz, C6D5Br, −20°C): l 7.22
(m, 2H, BCH2Ph), 7.10 (m, 1H, TiCH2Ph para-H), 7.07
(m, 2H, TiCH2Ph meta-H), 7.00 (m, 3H, BCH2Ph), 6.51
(d, 3JHH=6.0 Hz, 2H, TiCH2Ph ortho-H), 3.39 (br,
BCH2), 2.79 (s, 2H, TiCH2), 2.35 (s, 6H, NMe2), 1.61 (s,
15H, C5Me5). 13C-NMR (100.6 MHz, C6D5Br, −30°C):
1
l 148.68 (s, BCH2C6H5-ipso), 148.44 (d, JCF=239 Hz,
ortho-C6F5), 140.22 (d, 1JCF=243.9 Hz, para-C6F5),
136.63 (d, 1JCF=258.1 Hz, meta-C6F5), 132.85 (d,
1JCH=156 Hz), 132.36 (d, JCH=160 Hz), 132.17 (s,
1
1
TiCH2C6H5-ipso), 131.43 (d, JCH=162 Hz), 131.21 (d,
1JCH=165 Hz), 128.86 (d, JCH=166 Hz), 127.25 (s,
1
1
1
C5Me5), 122.96 (d, JCH=151 Hz), 92.17 (t, JCH=146
1
Hz, TiCH2), 44.91 (q, JCH=137 Hz, NMe2), 33.0 (br,
BCH2), 11.71 (q, 1JCH=128 Hz, C5Me5). 19F-NMR
(376.5 MHz, C6D5Br, −30°C): l -132.0 (ortho-C6F5),
−164.5 (para-C6F5), −167.3 (meta-C6F5).
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4. Supplementary material
Crystallographic data for the structural analysis of
Ti(h5-C5Me5)(NMe2)(CH2Ph)2 have been deposited with
the Cambridge Crystallographic Data Centre, CCDC,
no. 138218. Copies of this information may be obtained
free of charge from: The Director, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033
or e-mail: deposit@ccdc.cam.ac.uk or http://www.ccdc.
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Acknowledgements
This work was supported by the Fonds der Chemi-
.