A new class of mono- And tetra-nuclear titanatranes: Synthesis, structure, and ethylene polymerization studies. Role of single-sited active species?

Article abstract of DOI:10.1021/om034408r

Mono- and tetranuclear titanatranes bearing the C₃-symmetric aminotriol ligand N(CH₂-CHPhOH)₃ were synthesized. The structure of the tetratitanium compound was determined by single-crystal X-ray crystallography. The new ti

Full text of DOI:10.1021/om034408r

4462
Organometallics 2004, 23, 4462-4467
A New Cla ss of Mon o- a n d Tetr a -n u clea r Tita n a tr a n es:
Syn th esis, Str u ctu r e, a n d Eth ylen e P olym er iza tion
Stu d ies. Role of Sin gle-Sited Active Sp ecies?
Padmanabhan Sudhakar,† C. Valan Amburose,†
Govindarajan Sundararajan,*,† and Munirathinam Nethaji‡
Department of Chemistry, Indian Institute of Technology, Madras-600036, India, and
Department of Inorganic & Physical Chemistry, Indian Institute of Science,
Bangalore-560012, India
Received December 31, 2003
Mono- and tetranuclear titanatranes bearing the C3-symmetric aminotriol ligand N(CH2-
CHPhOH)3 were synthesized. The structure of the tetratitanium compound was determined
by single-crystal X-ray crystallography. The new titanatrane derivative included four
aminotriols ligated to four titanium atoms, forming a tetranuclear unit with µ2-O and µ3-O
bridges. The mono- and tetranuclear titanatranes were capable of polymerizing ethylene
with a turnover frequency of up to 375 kg of PE/((mol of catalyst) h bar). The polymers
obtained had Tm ≈ 133 °C, indicative of linear polyethylene, and were further characterized
by NMR. The ethylene polymerization activities of mono- and tetranuclear titanium catalysts
were related by a factor of 4, indicating possibly the formation of a common single-site active
species.
In tr od u ction
This is even more true when the correlation is evaluated
in the context of the superior control over polymer
architecture exhibited by the molecular symmetry of the
metallocene precatalysts.4 We recently employed pre-
catalysts based on Ti-containing C2-symmetric and C1-
symmetric (meso) aminodiolate ligands, for transfor-
mation reactions5a as well as for polymerization of
1-hexene.5b We also reported the production of highly
isotactic polyhexenes with the former catalyst, while the
latter catalyst yielded atactic polymers. As an extension,
we have initiated studies to evaluate the efficiency of
titanatranes containing a C3-symmetric trialkanolamine
ligand in olefin polymerization reactions.
Titanatranes containing triethanolamine ligands have
been synthesized and studied in detail by Verkade,6a-g
who has also employed these catalysts for production
of heterotactic-biased poly(rac-lactic acid). Half-sand-
wich titanocene compounds possessing trialkanolamine
ligands have been used as precatalysts for the syn-
diospecific polymerization of styrene.6h,i Chiral ti-
tanatranes of the type Ti[N(CH2CHRO)3]X, where R )
CH3, C6H5, C6H11 and X ) OiPr, Cl, were first synthe-
sized by Nugent and used in asymmetric catalysis.7
Here we report the synthesis of a new class of racemic
The past decade has witnessed a compelling series of
studies employing very efficient nonmetallocene cata-
lysts for olefin polymerization.1 Organometallic and
coordination compounds of early and late transition
metals containing noncyclopentadienyl ligands are gen-
erally the precatalysts, and their activation to polymer-
ize olefins has been usually effected by addition of
aluminum alkyls such as MAO or borate salts.2 One of
the attractive features of these nonmetallocene catalysts
is their ability to polymerize R-olefins in a living or
pseudo-living manner, and the polymers obtained in
general have been highly isotactic.3 Still, a comprehen-
sive correlation between the symmetry effects of the
ligand, and hence that of the precatalysts, with the
tacticity of the polyolefins produced is nearly absent.
* To whom correspondence should be addressed. E-mail: gsundar@
iitm.ac.in. Fax: 0091-44-22578241. Tel: 0091-44-22578254.
† Indian Institute of Technology.
‡ Indian Institute of Science.
(1) Gibson, V. C.; Spitzmesser, S. K. Chem. Rev. 2003, 103, 283.
(2) (a) Ittel, S. D.; J ohnson, L. K.; Brookhart, M. Chem. Rev. 2000,
100, 1169. (b) Chen, E. Y.; Marks, T. J . Chem. Rev. 2000, 100, 1391.
(3) For a review on living polymerization see: (a) Coates, G. W.;
Hustad, P. D.; Reinartz, S. Angew. Chem., Int. Ed. 2002, 41, 2236.
For examples of living polymerization of R-olefins with Zr and Hf
precatalysts with NON ligand systems see: (b) Liang, L.; Schrock, R.
R.; Davis, W. M.; McConville, D. H. J . Am. Chem. Soc. 1999, 121, 5797.
(c) Mehrkhodavandi, P.; Schrock, R. R.; Bonitatebus, P. J ., J r. Orga-
nometallics 2002, 21, 5785. (d) Mehrkhodavandi, P.; Schrock, R. R.;
Pryor, L. L. Organometallics 2003, 22, 4569. (e) Schrock, R. R.,
Adamchuk, J .; Ruhland, K.; Lopez, L. P. H. Organometallics 2003, 22,
5079. For examples of living polymerization of R-olefins with Zr
acetamidinates see: (f) J ayaratne, K. C.; Sita, L. R. J . Am. Chem. Soc.
2000, 122, 958. (g) Harney, M. B.; Keaton, R. J .; Sita, L. R. J . Am.
Chem. Soc. 2004, 126, 4536. For examples of living polymerization by
ligand structure modifications see: (h) Tshuva, E. Y.; Goldberg, I.; Kol,
M.; Goldschmidt, Z. Chem. Commun. 2001, 20, 2120. (i) Tshuva, E.
Y.; Groysman, S.; Goldberg, I.; Kol, M.; Goldschmidt, Z. Organome-
tallics 2002, 21, 662. (j) Groysman, S.; Goldberg, I.; Kol, M.; Genizi,
E.; Goldschmidt, Z. Organometallics 2003, 22, 3013.
(4) (a) Ewen, J . A.; J ones, R. L.; Razavi, A.; Ferrara, J . D. J . Am.
Chem. Soc. 1988, 110, 6255. (b) Brintzinger, H. H.; Fisher, D.;
Mulhaupt, R.; Rieger, B.; Waymouth, R. M. Angew. Chem., Int. Ed.
Engl. 1995, 34, 1143.
(5) (a) Manivannan, R.; Sundararajan, G., Kaminsky, W. Macromol.
Rapid Commun. 2000, 21, 968. (b) Manivannan, R.; Sundararajan, G.
Macromolecules 2002, 35, 7883.
(6) (a) Menge, W. M. P. B.; Verkade, J . G. Inorg. Chem. 1991, 30,
4628. (b) Naiini, A. A.; Menge, W. M. P. B.; Verkade, J . G. Inorg. Chem.
1991, 30, 5009. (c) Naiini, A. A.; Ringrose, S. L.; Su, Y.; J acobson, R.
A.; Verkade, J . G. Inorg. Chem. 1993, 32, 1290. (d) Kim, Y.; Verkade,
J . G. Organometallics 2002, 21, 2395. (e) Kim, Y.; J naneshwara, G.
K.; Verkade, J . G. Inorg. Chem. 2003, 42, 1437. (f) Kim, Y.; Hong, E.;
Lee, M. H.; Kim, J .; Han, Y.; Do, Y. Organometallics 1999, 18, 36. (g)
Kim, Y.; Do, Y. J . Organomet. Chem. 2002, 655, 186.
10.1021/om034408r CCC: $27.50 © 2004 American Chemical Society
Publication on Web 08/07/2004

Mono- and Tetranuclear Titanatranes
Organometallics, Vol. 23, No. 19, 2004 4463
Sch em e 1. Syn th esis of Liga n d s 1 a n d 2 a n d th e Mon on u clea r Tita n a tr a n e 4
Sch em e 2. Syn th esis of th e Tetr a n u clea r Tita n iu m
P r eca ta lyst a n d Gen er a tion of a Com m on
Mon otita n a te Active Sp ecies for Eth ylen e
P olym er iza tion
titanatranes containing the tetradentate oxoamine
ligands N(CH2CH(Ph)OH)3 (C3-1 and Cs-2). We have
also discovered that partial hydrolysis of the mono-
nuclear ligand 1 containing a Ti-chloro compound (4)
gives a crystalline tetranuclear titanatrane (5). Such
formation of multinuclear titanatranes from the con-
trolled hydrolysis of a mononuclear triethanolamine
titanium compound has been reported,8 though forma-
tion of a tetranuclear intermediate has not been ob-
served thus far under these conditions. In the present
investigation, we wish to report the initial results on
the performance of these precatalysts 4 and 5 upon
activation with MAO for ethylene polymerization.
Resu lts a n d Discu ssion
A diastereomeric mixture containing C3 (1) and Cs (2)
ligands was obtained by reacting 3 equiv of styrene
oxide with 1 equiv of NH3 in methanol. The preparation
of an optically pure methyl analogue of 1 was first
reported by Morrison9 and then modified by Nugent.7
We find that it is convenient to synthesize the required
aminotriols in a mixture of both C3 and Cs forms using
racemic styrene oxide and ammonia (Scheme 1). After
removal of side products containing unwanted amino
alcohols by flash chromatography, the ligand 1 was
isolated as colorless crystals from a 50:50 solution of
toluene and hexane and was further purified by recrys-
tallization from 2-propanol. The mother liquor was
subjected to semipreparative HPLC using 80:20 mixture
of methanol and water for separation of the ligands 1
and 2.
indicated in Scheme 1, with the proton signals shifting
downfield by approximately 1.00 ppm relative to the free
ligand, and a somewhat smaller downfield shift of 0.4-
0.8 ppm was observed for the CH2N resonances.
The titanium chloride compound 4, in the presence
of 0.5 equiv of water, underwent partial hydrolysis, as
shown in Scheme 2, yielding the new class of titanatrane
5 as colorless crystals. Addition of more than 0.5 equiv
of water yielded amorphous materials that exhibit low
solubility in common organic solvents, rendering further
characterization difficult.
Cr ysta l a n d Molecu la r Str u ctu r e of {Ti2[N(CH2-
CHP h O)3]2(µ3-O)}2 (5). The outcome of our X-ray
structural analysis revealed that 5 is a tetranuclear Ti
compound containing two Ti2[N(CH2CHPhO)3]2 units
which are linked by a pair of triply bridging oxo ligands
with four solvated water molecules. The ORTEP draw-
ing is depicted in Figure 1. The crystallographic data
and selected interatomic distances and angles are
provided in Tables 1 and 2, respectively. The geometry
around each Ti can be viewed as a distorted octa-
hedron, similar to that found in [Ti3(µ2-O){OCH-
(CH3)2}{(OCH2CH2)2(µ2-OCH2CH2)N}2{(OCH2CH2)(µ2-
OCH2CH2)2N}]2.8
When 1 was treated with 1 equiv of Ti(OiPr)4 in
toluene, the reaction proceeded with a loss of 3 equiv of
1
2-propanol. The H and 13C NMR spectra indicated the
formation of the compound and the accompanying
symmetric nature in the solution state. Treatment of
this titanium isopropoxide compound 3 with CH3COCl
in toluene resulted in the formation of 4 in 65% yield.
The crystal structure of the methyl analogue was
1
reported by Nugent in 1994.7 The H NMR spectrum of
compound 4 was consistent with the proposed structure
In Ti(2) and Ti(3) the axial sites are occupied by two
oxygen atoms of the tripodal ligand 1 and the equatorial
planes are occupied by oxygen, nitrogen atoms of 1, and
the two oxygen atoms which are introduced by hydroly-
sis. In the case of Ti(1) and Ti(4) the axial sites are
occupied by two oxygen atoms of 1, while the equatorial
planes are occupied by oxygen, the nitrogen of 1, an
oxygen atom of the neighbor ligand, and an oxygen atom
introduced via hydrolysis. Among the four titanium
atoms, Ti(2) and Ti(3) are in similar coordination
(7) (a) Nugent, W. A.; Harlow, R. L. J . Am. Chem. Soc. 1994, 116,
6142. (b) Bonchio, M.; Calloni, S.; Furia, F. D.; Licini, G.; Modena, G.;
Moro, S.; Nugent, W. A. J . Am. Chem. Soc. 1997, 119, 6935. (c) Bonchio,
M.; Licini, G.; Bortolini, O.; Moro, S.; Nugent, W. A. J . Am. Chem.
Soc. 1999, 121, 6258.
(8) Kemmitt, T.; Al-Salim, N. I.; Gainsford, G. J . Inorg. Chem. 2000,
39, 6067.
(9) Morrison, J . D.; Grandbois, E. R.; Weisman, G. R. In Asymmetric
Reactions and Processes in Chemistry; Eliel, E. L., Otsuka, S., Eds.;
ACS Symposium Series 185; American Chemical Society: Washington,
DC, 1982.

4464 Organometallics, Vol. 23, No. 19, 2004
Sudhakar et al.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for 5a
Ti(1)-Ti(3)
Ti(2)-Ti(3)
3.175(3)
3.107(3)
Ti(2)-Ti(4)
3.177(3)
Ti(1)-N(1)
Ti(2)-N(3)
2.402(8)
2.331(8)
Ti(3)-N(2)
Ti(4)-N(4)
2.352(8)
2.427(8)
Ti(1)-O(5)
Ti(2)-O(5)
1.925(7)
1.973(6)
Ti(3)-O(5)
1.934(7)
Ti(2)-O(9)
Ti(3)-O(9)
1.936(6)
2.013(6)
Ti(4)-O(9)
1.900(6)
Ti(1)-O(4)
Ti(3)-O(4)
2.138(7)
2.014(7)
Ti(2)-O(11)
Ti(4)-O(11)
2.026(6)
2.134(7)
Ti(1)-O(1)
Ti(1)-O(2)
Ti(1)-O(3)
Ti(2)-O(6)
Ti(2)-O(10)
1.902(7)
1.837(9)
1.853(9)
1.802(8)
1.837(8)
Ti(3)-O(7)
Ti(3)-O(8)
Ti(4)-O(12)
Ti(4)-O(14)
Ti(4)-O(13)
1.829(8)
1.855(8)
1.838(9)
1.845(8)
1.883(8)
O(2)-Ti(1)-O(3)
O(2)-Ti(1)-O(1)
O(3)-Ti(1)-O(1)
O(2)-Ti(1)-O(5)
O(3)-Ti(1)-O(5)
O(1)-Ti(1)-O(5)
O(2)-Ti(1)-O(4)
O(3)-Ti(1)-O(4)
O(1)-Ti(1)-O(4)
O(5)-Ti(1)-O(4)
O(2)-Ti(1)-N(1)
O(3)-Ti(1)-N(1)
O(1)-Ti(1)-N(1)
O(5)-Ti(1)-N(1)
O(4)-Ti(1)-N(1)
136.2(4)
102.3(4)
98.7(4)
103.5(3)
114.4(4)
90.4(3)
87.1(3)
84.2(3)
162.1(3)
72.5(3)
75.4(3)
73.1(4)
76.0(3)
165.6(3)
121.5(3)
O(12)-Ti(4)-O(14) 134.8(4)
O(12)-Ti(4)-O(13) 100.4(4)
O(14)-Ti(4)-O(13) 101.7(4)
O(12)-Ti(4)-O(9)
O(14)-Ti(4)-O(9)
O(13)-Ti(4)-O(9)
O(12)-Ti(4)-O(11)
O(14)-Ti(4)-O(11)
112.5(3)
107.2(4)
88.0(3)
83.5(3)
88.8(3)
F igu r e 1. ORTEP drawing of 5.
Ta ble 1. Cr ysta llogr a p h ic Da ta for 5
O(13)-Ti(4)-O(11) 159.9(3)
formula
fw
cryst syst
space group
a, Å
C96H104N4O18Ti4
O(9)-Ti(4)-O(11)
O(12)-Ti(4)-N(4)
O(14)-Ti(4)-N(4)
O(13)-Ti(4)-N(4)
O(9)-Ti(4)-N(4)
O(11)-Ti(4)-N(4)
72.4(2)
73.7(3)
73.7(3)
76.8(3)
164.5(3)
123.0(3)
1793.43
orthorhombic
P212121
13.465(5)
27.531(1)
29.197(1)
90
b, Å
c, Å
R, deg
O(6)-Ti(2)-O(10)
O(6)-Ti(2)-O(9)
O(10)-Ti(2)-O(9)
O(6)-Ti(2)-O(5)
O(10)-Ti(2)-O(5)
O(9)-Ti(2)-O(5)
O(6)-Ti(2)-O(11)
135.7(3)
105.7(3)
116.5(3)
89.8(3)
88.1(3)
75.6(3)
O(7)-Ti(3)-O(8)
O(7)-Ti(3)-O(5)
O(8)-Ti(3)-O(5)
O(7)-Ti(3)-O(9)
O(8)-Ti(3)-O(9)
O(5)-Ti(3)-O(9)
O(7)-Ti(3)-O(4)
O(8)-Ti(3)-O(4)
O(5)-Ti(3)-O(4)
O(9)-Ti(3)-O(4)
O(7)-Ti(3)-N(2)
O(8)-Ti(3)-N(2)
O(5)-Ti(3)-N(2)
O(9)-Ti(3)-N(2)
O(4)-Ti(3)-N(2)
135.4(3)
106.6(4)
115.5(4)
89.7(3)
87.8(3)
74.7(3)
103.1(4)
101.1(3)
75.2(3)
149.5(3)
74.5(4)
76.1(4)
150.4(3)
134.6(3)
75.8(3)
â, deg
90
90
γ, deg
V, Å3
10 823(7)
4
293(2)
1.101
0.343
0.3 × 0.3 × 0.25
2.53-23.33
67 119
15 619
0.1986
Z
T (K)
F, Mg m-3
µ, mm-1
cryst size, mm
θ range, deg
no. of rflns collected
no. of unique data
Rint
103.2(4)
O(10)-Ti(2)-O(11) 100.8(3)
O(9)-Ti(2)-O(11)
O(5)-Ti(2)-O(11)
O(6)-Ti(2)-N(3)
O(10)-Ti(2)-N(3)
O(9)-Ti(2)-N(3)
O(5)-Ti(2)-N(3)
O(11)-Ti(2)-N(3)
74.1(3)
149.3(3)
76.1(3)
74.5(3)
149.3(3)
135.0(3)
75.6(3)
refinement method
full-matrix-block
least squares on F2
1098
no. of params
no. of restraints
goodness of fit on F2
R1a
C(9)-N(1)-C(17)
C(9)-N(1)-C(8)
C(17)-N(1)-C(8)
C(65)-N(2)-C(32)
C(65)-N(2)-C(33)
C(32)-N(2)-C(33)
C(25)-O(4)-Ti(3)
C(25)-O(4)-Ti(1)
Ti(3)-O(4)-Ti(1)
Ti(1)-O(5)-Ti(3)
Ti(1)-O(5)-Ti(2)
Ti(3)-O(5)-Ti(2)
113.2(9)
C(73)-N(4)-C(81)
117.1(6)
112.0(6)
111.7(6)
108.9(8)
113.4(9)
115.6(8)
0
114.7(10) C(73)-N(4)-C(89)
110.8(10) C(81)-N(4)-C(89)
111.0(9)
114.9(8)
0.972
0.1094
0.2771
0.976 and -0.400
wR2b
C(48)-N(3)-C(57)
C(48)-N(3)-C(49)
largest diff Fourier peaks
and holes, e Å-3
109.8(10) C(57)-N(3)-C(49)
119.5(7)
128.4(6)
99.7(3)
110.7(3)
141.7(4)
105.3(3)
C(58)-O(11)-Ti(2) 118.8(4)
C(58)-O(11)-Ti(4) 125.8(4)
R1 ) ∑|Fo - Fc|/∑|Fo|. wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]]1/2
.
a
b
Ti(2)-O(11)-Ti(4)
Ti(4)-O(9)-Ti(2)
Ti(4)-O(9)-Ti(3)
Ti(2)-O(9)-Ti(3)
99.5(3)
111.8(3)
142.2(4)
103.7(3)
environments, both lending one of their oxo arms for
double bridging, and are separated by a Ti(2)‚‚‚Ti(3)
distance of 3.107(3) Å, which is the shortest among the
three Ti‚‚‚Ti distances (Table 2). All four titanium
atoms, the four bridging oxygen atoms, and the four
nitrogen atoms are almost in a plane. Among the four
Ti-N bonds, two are longer (Ti(4)-N(4) ) 2.424(8) Å
and Ti(1)-N(1) ) 2.402 (8) Å) than the other two (Ti-
(2)-N(3) ) 2.331(8) Å and Ti(3)-N(2) ) 2.352 (8) Å).
However, one of the Ti-N bonds, Ti(4)-N(4), is slightly
longer (not within (3σ) than the reported Ti-N bond
lengths (range 2.293(3)-2.400(3) Å) for triethanolami-
notitanatranes.8,10 The average Ti-O bond length,
a
Symmetry transformations were used to generate equivalent
atoms.
excluding Ti-O bridging distances, is 1.876(8) Å. To our
knowledge, this is the first example of a tetranuclear
titanium network containing a C3-symmetric ligand.
Ca ta lytic Activity in th e Eth ylen e P olym er iza -
tion P r ocess. The catalytic activity in the ethylene
polymerization of 4 and 5, in association with MAO, was
studied, and the results are summarized in Table 3.
Polymerization reactions were carried out in the tem-
perature range of 0-70 °C and at several Al/Ti molar
ratios. While no induction period was observed for any
(10) Dunn, S. C.; Mountford, P.; Robson, D. A. J . Chem. Soc., Dalton
Trans. 1997, 293.

Mono- and Tetranuclear Titanatranes
Organometallics, Vol. 23, No. 19, 2004 4465
Ta ble 3. P olym er iza tion of Eth ylen e w ith 4/MAO
a n d 5/MAOa
c
d
temp
(°C)
pressure
(bar)
yield
(g)
Tm
Mη
activityb
(°C)
(kg/mol)
Catalyst 4/MAO
30
30
30
0
10
50
60
70
1
2
3
1
1
1
1
1
2.5
3.4
3.9
3.7
3.0
3.0
1.6
0.5
250
170
130
375
300
300
160
50
136
138
141
136
134
133
133
132
625
800
1010
420
550
380
290
210
Catalyst 5/MAO
30
30
30
0
10
50
60
70
1
2
3
1
1
1
1
1
0.7
1.1
1.2
0.8
0.7
0.8
0.8
0.4
70
55
40
80
74
80
85
40
135
133
132
136
135
134
130
132
330
450
620
205
250
370
410
280
F igu r e 2. Temperature dependence on catalytic activity.
a
Polymerization conditions: [4] ) 1.09 × 10-5 mol; [5] ) 0.27
× 10-5 mol; Al/Ti ) 200; solvent toluene. In units of kg of PE/
b
width of 1000 Hz (with respect to TiCl4 as external
standard). A strikingly similar spectrum of two signals
at 870 and 1070 ppm with a line width of 1000 Hz
attributable respectively to 47Ti and 49Ti nuclei was seen
when 4 in toluene was treated with MAO. We surmise,
therefore, that both the tetranuclear 5 and the mono-
nuclear 4 give rise to the same or similar cationic
titanium species. At present we are not sure if this
indeed is the active species for catalysis, as the metal
center lacks the required number of vacant coordination
sites. However, the removal of a ligated oxygen atom
by MAO, to facilitate the approach of monomer ethylene,
also cannot be ruled out. For example, Eisen has
explained the reactivity of a C3-symmetric zirconium
catalyst attached to three benzamidinate ligands, by
removing one of the ligating units from the metal center
by MAO.12a Another recent report on ostensibly similar
titanium(IV) compounds of triaryloxoamine ligands
suggests a delinking of the metal-oxygen bond prior
to initiating ethylene polymerization.12b Bruno12c offers
a similar route for styrene polymerization by a titanium
compound containing tripodal aryloxide ligands in the
presence of MAO.
The polyethylenes obtained had good solubility in
o-dichlorobenzene, 1,2,4-trichlorobenzene, xylene, mesi-
tylene, etc. at high temperatures (>100 °C). The 13C
NMR of the polyethylene obtained showed a single peak
at 28.27 ppm, and the melting points of polymers
obtained from DSC studies were in the region 130-135
°C, consistent with a linear polyethylene architecture.
Varying the ethylene pressures (1-3 bar) and polym-
erization temperatures has no effect on the linearity of
the resultant polyethylene, whereas Mη was found to
increase with increasing pressure (Table 3).
((mol of catalyst) h bar). c Determined from differential scanning
d
calorimetry. From intrinsic viscosity using a Ubbelohde viscom-
eter at 135 °C.
of the polymerization reactions, it was also found that
the polymerization rate increased for the first 10 min,
after which time it remained constant. It can be seen
from Table 3 that at a constant Al/Ti ratio, while the
temperature was increased to 50 °C, led to an increase
in the polymerization rate. At higher temperatures a
decrease in activity was observed, and this might be
related to the thermal instability of the precatalyst or
that of the active species at higher temperatures. The
optimal temperature for each system depended on the
balance between the propagation rate and the thermal
instability. For instance, the polymerization activity of
the system based on compound 5 was still increasing
at the highest temperature used (i.e., 60 °C).
In all cases, the polymerization activity of compound
4 was 4 times greater than that observed for compound
5 (except at higher temperatures, >50 °C). In other
words, the activity per titanium atom was the same for
both compounds, indicating possibly that the tetra-
nuclear species is cleaved into mononuclear cationic
species in the presence of MAO. For example, at 30 °C
titanatrane 5 showed an activity of around 70 kg of PE/
((mol of titanatrane) h bar) (which corresponds to four
titanium atoms) that upon normalization to one tita-
nium atom gives an activity of 280 kg of PE/((mol of
catalyst) h bar), which is of the same order of activity
observed for the mononuclear titanatrane 4 (∼250 kg
of PE/((mol of catalyst) h bar)). The actual and normal-
ized activities of the catalysts obtained from 4 and 5
with MAO are compared in Figure 2 as a function of
polymerization temperature. The temperature depen-
dence of the activities for the mononuclear catalyst 4 is
easily simulated by 5 when its own activity is multiplied
by a factor of 4.
Con clu sion
To summarize, we have synthesized and character-
ized two novel titanatrane compounds bearing a C3-
Our attempts to examine the structures of the com-
pounds 4 and 5 by solution Ti NMR failed, possibly
because of the distorted-octahedral structure of the
titanium atoms.11 Surprisingly, however, when a solu-
tion of 5 in toluene was treated with MAO in toluene,
the 47Ti signal appeared at -875 ppm with a line width
of 1000 Hz and a 49Ti signal at -1075 ppm with a line
(11) (a) Boyle, T. J .; Alamond, T. H.; Mechenbier, E. R. Inorg. Chem.
1997, 36, 3293. (b) Foris, A. Magn. Reson. Chem. 2000, 38, 1044.
(12) (a) Averbuj, C.; Tish, E.; Eisen, M. S. J . Am. Chem. Soc. 1998,
120, 8640. For the suggestion of a formal loss of an aryloxide arm of a
tripodal ligand from the metal center during polymerization, see: (b)
Wang, W.; Fujiki, M.; Nomura, K. Macromol. Rapid Commun. 2004,
25, 504. (c) Michalczyk, L.; Gala, S.; Bruno, J . W. Organometallics
2001, 20, 5547.

4466 Organometallics, Vol. 23, No. 19, 2004
Sudhakar et al.
127.9 (Ph C), 141.4 (Ph C). IR (CH2Cl2, cm-1): 3400, 3020,
2880, 1600, 1490, 1450, 1220, 1200, 1050, 887. Anal. Calcd
for C24H27NO3: C, 76.39; H, 7.16; N, 3.71. Found: C, 76.16;
H, 7.31; N, 3.66.
symmetric aminotriol ligand. The compounds polymer-
ize ethylene with high catalytic activities, and the
polymerization data suggest the formation of mono-
nuclear catalytically active species from a tetranuclear
system. Further studies to understand the nature of the
active species in polymerization and to evaluate the use
of these precatalysts for polymerization of R-olefins are
in progress.
Syn th esis of 3. A solution of 1 (3.8 g, 10 mmol) in diethyl
ether (10 mL) was added to a solution of Ti(OiPr)4 (2.84 g, 10
mmol) in toluene (20 mL) at -78 °C. The mixture was stirred
for 3 h at room temperature. Removal of the solvent afforded
the titanium isopropoxide compound 3 (4.3 g, 90%) as a white
1
solid. H NMR (400 MHz, CDCl3): δ1.22 (d, J ) 7.4, 3, CH3,
6H), 3.15-3.40 (m, N-CH2, 6H), 5.20 (septet, J ) 4.2, 3,
CH(CH3)2, 1H), 5.95 (m, Ph-CH-O, 3H), 7.38-7.84 (m, Ph,
15H). 13C NMR (100 MHz, CDCl3): δ 25.1 (CH3), 63.8 (N-
CH2), 71.1 (CH(CH3)2), 81.3 (O-CH), 125.9 (Ph C), 127.4 (Ph
C), 128.4 (Ph C), 142.2 (Ph C). IR (CH2Cl2, cm-1): 3270, 3048,
2973, 1754, 1494, 1454, 1374, 1219, 1067, 946, 850. Anal. Calcd
for C27H31NO4Ti: C, 67.36; H, 6.49; N, 2.91. Found: C, 67.41;
H, 6.53; N, 2.90.
Exp er im en ta l Section
Gen er a l P r oced u r es. All manipulations were done under
an atmosphere of dry, oxygen-free argon employing vacuum
or Schlenk line techniques, unless otherwise stated. Argon was
purified by passage through columns of MnO anchored on
silica gel catalyst13 and 4 Å molecular sieves. All polymeriza-
tions were performed in a Buchi type I high-pressure reactor
1
equipped with BDS (Buchi Database System). H NMR (400
Syn th esis of 4. The Ti isopropoxide compound 3 (4.6 g, 10.0
mmol) prepared as shown above was dissolved in toluene (25
mL), and acetyl chloride (0.98 g, 12.5 mmol) was added. The
mixture was stirred at room temperature for 2 h to give a clear
yellow solution and was precipitated in hexane. Hexane was
removed by cannula, and the white solid was redissolved in
CH2Cl2 and reprecipitated in hexane. Removal of the solvent
afforded a white solid (3 g, 65%) that was dried under vacuum.
1H NMR (400 MHz, CDCl3): δ 3.21-3.52 (m, N-CH2, 6H),
5.95 (m, O-CH, 3H), 7.38-7.84 (m, Ph, 15H). 13C NMR (100
MHz, CDCl3): δ 63.8 (N-CH2), 81.3 (O-CH), 125.9 (Ph C),
127.4 (Ph C), 128.4 (Ph C), 142.2 (Ph C). IR (CH2Cl2, cm-1):
3267, 3052, 2973, 1753, 1494, 1454, 1374, 1220, 1067, 946, 849.
Anal. Calcd for C24H24NO3TiCl: C, 62.34; H, 5.24; N, 3.06.
Found: C, 61.64; H, 5.32; N, 3.28.
MHz) and 13C NMR (100 MHz) spectra were recorded in CDCl3
at ambient temperature with tetramethylsilane (TMS) as the
internal standard, and 47Ti NMR (22.5 MHz) spectra were
recorded with TiCl4 as an external standard using a Bruker
AV400 spectrometer. 13C NMR spectra of polyethylene samples
were obtained in 1,2,4-trichlorobenzene at 120 °C with DMSO-
d6 as lock solvent under the following conditions: pulse angle
25°, acquisition time 0.655 s, pulse delay 6 s, and number of
scans 6000. Intrinsic viscosities of the polyethylene samples
were determined by dissolving 10 mg of polymer in 20 mL of
Decalin (98% cis/trans) using an Ubbelohde viscometer kept
at 135 °C. Thermal analyses were performed on a Stanton
Redcrofts simultaneous thermal analyzer (781 series). Flash
chromatography was carried out on 230-400 mesh silica gel
following the procedure of Still.14 IR spectra of samples were
recorded as CH2Cl2 solutions on a J ASCO FTIR 400 spectrom-
eter.
Syn th esis a n d Isola tion of Liga n d s 1 a n d 2. To 2 M
ammonia in methanol solution (7.0 mL, 14.0 mmol) was added
styrene epoxide (5.0 g, 41.6 mmol) at -78 °C. The mixture was
stirred overnight at room temperature and then heated in an
80 °C oil bath for 4 days. The product was obtained as a
colorless syrupy liquid. The diastereomeric mixture containing
the C3-symmetric ligand 1 and Cs-symmetric ligand 2 was
purified from other impurities by flash chromatography using
70:30 hexane-ethyl acetate (yield: 60%). This mixture was
further dissolved in 50:50 toluene-hexane under hot condi-
tions and cooled to room temperature. Ligand 1 crystallizing
out as colorless crystals was further purified by repeated
crystallization from 2-propanol solution. Ligand 2 was freed
from residual 1 using semipreparative HPLC using 80:20
methanol-water mixture. The overall yields of 1 and 2 were
20% and 42%, respectively.
Syn th esis of th e Tetr a n u clea r Ti Com p ou n d 5. The
mononuclear compound 4 (4.57 g, 10.0 mmol) was dissolved
in toluene (10 mL) and distilled water (5.0 mmol). The reaction
mixture was stirred at room temperature for 30 min, and the
toluene was removed by distillation under reduced pressure.
The product separated from the residual toluene as a viscous
liquid and slowly crystallized on cooling. 5: yield 2.465 g, 55%.
1H NMR (400 MHz, CDCl3): δ 3.12-3.60 (m, N-CH2, 6H),
6.12 (m, O-CH, 3H), 7.21-7.80 (m, Ph, 15H). 13C NMR (100
MHz, CDCl3): δ 64.1 (N-CH2), 81.7 (O-CH), 126.2 (Ph C),
127.9 (Ph C), 128.7 (Ph C), 142.9 (Ph C). IR (CH2Cl2, cm-1):
3244, 3053, 2970, 1958, 1754, 1603, 1533, 1494, 1453, 1374,
1219, 1065, 943, 913, 847. Anal. Calcd for C96H96N4O14Ti4: C,
66.99; H, 5.58; N, 3.25. Found: C, 65.43; H, 5.47; N, 3.33.
Eth ylen e P olym er iza tion . An autoclave of capacity 1 L
was dried under vacuum (10-1 mmHg) for several hours.
Toluene (300 mL) was transferred into the vessel under a
positive pressure of nitrogen and was heated to 30 °C. The
temperature was controlled (to ca. (2 °C) with an external
heating/cooling bath and was monitored by a thermocouple
that extended into the polymerization vessel. A solution of
MAO in toluene was then injected, and the mixture was stirred
for 3 min at 200 rpm. The precatalyst in a solution of toluene
was then injected, and the reaction mixture was stirred for
an additional 3 min at the same rate. The rate of stirring was
increased to 1000 rpm, and the vessel was vented of nitrogen
and pressurized with ethylene. Any recorded exotherm was
within the allowed temperature differential of the heating/
cooling system. The solution was stirred for 1 h, after which
time the reaction was quenched with 1 M HCl in MeOH. The
precipitated polymer was subsequently washed with MeOH
and dried at 100 °C for at least 24 h prior to weighing.
X-r a y Cr ysta llogr a p h ic Da ta Collection a n d Refin e-
m en t of Str u ctu r e. Colorless crystals of the compound 5,
suitable for X-ray diffraction studies, were grown by slow
evaporation of a toluene-hexane (10:1) mixture. A crystal of
approximate size 0.3 × 0.3 × 0.25 mm3 was mounted in a
Lindemann tube with paraffin oil to protect it from atmo-
1 was obtained as colorless needlelike crystals. Mp: 142-
144 °C. 1H NMR (400 MHz, CDCl3): δ 2.73 (dd, J ) 7.2, 2,
N-CH2, 3H), 2.97 (dd, J ) 7.4, 4, N-CH2, 3H), 5.00 (dd, J )
3.5, 4, O-CH, 3H), 5.22-5.71 (br s, C-OH, 3H), 7.28-7.44
(m, Ph, 15H). 13C NMR (100 MHz, CDCl3): δ 63.6 (N-CH2),
70.5 (O-CH), 126.0 (Ph C), 127.6 (Ph C), 128.4 (Ph C), 141.8
(Ph C). IR (CH2Cl2, cm-1): 3427, 3031, 2888, 1603, 1494, 1453,
1334, 1201, 1063, 887. Anal. Calcd for C24H27NO3: C, 76.39;
H, 7.16; N, 3.71. Found: C, 76.26; H, 7.08; N, 3.78.
1
2 was obtained as a colorless syrupy liquid. H NMR (400
MHz, CDCl3): δ 2.82-2.87 (m, N-CH2, 6H), 4.21-4.84 (br s,
C-OH, 3H), 4.77-4.81 (m, O-CH, 3H), 7.26-7.35 (m, Ph,
15H). 13C NMR (100 MHz, CDCl3): δ 65.1 (N-CH2), 65.4 (N-
CH2), 71.7 (O-CH), 73.6 (O-CH), 125.5 (Ph C), 127.1 (Ph C),
(13) (a) Shriver, D. F.; Drezdzen, M. A. The Manipulation of Air-
Sensitive Compounds, 2nd ed.; Wiley: New York, 1986; Chapter 3. (b)
Sundararajan, G.; Shivasubramaniam, V. Res. Ind. 1991, 36, 26.
(14) Still, W. C.; Kahn, M.; Mitra, A. J . J . Org. Chem. 1978, 48,
2923.

Mono- and Tetranuclear Titanatranes
Organometallics, Vol. 23, No. 19, 2004 4467
spheric air and moisture during data collection. The X-ray
diffraction data at room temperature were measured in frames
with increasing ω (width, 0.3°/frame) at a scan speed of 8
s/frame using a Bruker SMART APEX CCD diffractometer,
equipped with a fine-focus sealed-tube X-ray source. The
SMART software was used for data acquisition and the SAINT
software for data extraction. The structure was solved by the
heavy-atom method and refined by full-matrix least squares
using the SHELX system of programs.15 All non-hydrogen
atoms were refined anisotropically. The hydrogen atoms
attached to carbon atoms in the compound were generated and
assigned isotropic thermal parameters, riding on their parent
carbon atoms, and used for structure factor calculation only.
The hydrogen atoms of the ligands were located from the
difference Fourier maps, and they were refined for two cycles
isotropically at the initial stage. At the final stage of refine-
ment, their thermal parameters were only refined isotropically.
Ack n ow led gm en t. This research was funded by the
Department of Science & Technology (SP/S-1/G-08/99)
and Reliance Industries Limited. N. Chandrakumar (IIT
Madras) is also thanked for discussions related to 47Ti
NMR studies.
Su p p or tin g In for m a tion Ava ila ble: A CIF file giving
crystallographic data for compound 5. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
(15) Sheldrick, G. M. SHELX-97: Programs for Crystal Structure
Solution and Refinement; University of Go¨ttingen, Go¨ttingen, Ger-
many, 1997.
OM034408R