Post-metallocenes: New bis(pyrrolyl-2-aldiminato) titanium complexes for ethylene polymerization

Article abstract of DOI:10.1246/cl.2000.1270

Two new bis(pyrrolyl-2-aldiminato) titanium complexes were synthesized and their structures determined by X-ray analyses. These complexes displayed high ethylene polymerization activity using MAO or Ph₃C⁺B^-(C₆F₅)₄ /ⁱBu₃Al as a cocatalyst. One of the complexes exhibited very high ethylene polymerization activity (14100 kg-polymer-mol-Ti^-1·h^-1) with very high molecular weight (M_v: 260.1 × 10⁴) using MAO as a cocatalyst.

Full text of DOI:10.1246/cl.2000.1270

1270
Chemistry Letters 2000
Post-Metallocenes: New Bis(pyrrolyl-2-aldiminato) Titanium Complexes
for Ethylene Polymerization
Yasunori Yoshida, Shigekazu Matsui, Yukihiro Takagi, Makoto Mitani, Masatoshi Nitabaru,
Takashi Nakano, Hidetsugu Tanaka, and Terunori Fujita*
Material Science Laboratory, Mitsui Chemicals, Inc., 580-32 Nagaura, Sodegaura, Chiba 299-0265
(Received August 9, 2000; CL-000762)
Two new bis(pyrrolyl-2-aldiminato) titanium complexes
were synthesized and their structures determined by X-ray
analyses. These complexes displayed high ethylene polymer-
ization activity using MAO or Ph3C+B–(C6F5)4/iBu3Al as a
cocatalyst. One of the complexes exhibited very high ethylene
polymerization activity (14100 kg-polymer·mol-Ti–1·h–1) with
very high molecular weight (Mv: 260.1 × 104) using MAO as a
cocatalyst.
line in 65% yield. Treatment of 2 equiv of lithium salt of N-(2-
pyrrolidene)aniline with TiCl4 in dry diethyl ether furnished
complex 1 in 79% yield as a black powder. Likewise, complex
2 was synthesized in a similar manner.
As a result of X-ray analyses, complexes 1 and 2 were
revealed to have a similar stereochemical structure (complex 1:
Figure 1).9 That is to say, they adopted a distorted octahedral
structure around the titanium center. A pyrrole group is
attached to the titanium metal by virtue of not π-bonding but σ-
bonding. Two pyrrole-nitrogen atoms were situated in trans-
position. Alternatively, two imine-nitrogen atoms were located
cis to one another, and two chlorine atoms, potential olefin
polymerization sites, were also located cis to one another.
After the sensational discovery1 of highly active group 4
metallocene catalysts, much effort has been devoted to the
research on well-defined transition metal complexes with a
view to acquiring new olefin polymerization catalysts.2 In con-
sequence, a certain number of high performance olefin poly-
merization catalysts based on late transition metals have been
developed.3 However, till recently, other than group 4 metal-
locene catalysts, little has been known about group 4 transition
metal complexes which display high catalytic performance for
olefin polymerization. Very recently, we found zirconium
complexes with two bidentate salicylaldimine ligands, which
display exceptionally high ethylene polymerization activity, as
a result of the study of group 4 transition metal complexes hav-
ing multidentate and non-symmetric ligands.4 Alternatively, a
number of titanium complexes which possess intriguing catalyt-
ic properties for olefin polymerization have been reported.5
There are, however, only a few examples of titanium complexes
displaying high ethylene polymerization activity,6 though titani-
um is a major player in highly active solid Ziegler–Natta cata-
lysts. At this time, we have found highly active new titanium
complexes possessing two pyrrolide-imine ligands,7 they being
multidentate and non-symmetric ligands.8 Therefore, in this
paper, we would like to describe these titanium complexes.
A general synthetic route for titanium complexes having
two pyrrolide-imine ligands is shown in Scheme 1. For
instance, complex 1 was prepared as follows: Reaction of pyr-
role-2-carboxyaldehyde with aniline in dry EtOH using formic
acid as a catalyst at rt for 72 h afforded N-(2-pyrrolidene)ani-
An active species of group 4 transition metal complexes for
olefin polymerization is known to be an alkyl cationic
complex.10 Thus, the structure of a methyl cationic complex
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
1271
3
4
a) L. K. Johnson, C. M. Killian, and M. S. Broookhart, J. Am.
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of the 3rd Seminar on Science and Technology – Catalysis – ,
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Tanaka, T. Nakano, and T. Fujita, Chem. Lett., 2000, 554. e) S.
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J. Schattenmann, R. R. Schrock, and W. M. Davis,
Organometallics, 17, 989 (1998).
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M. Nitabaru, T. Nakano, and T. Fujita, Chem. Lett., 1999, 1065. b)
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generated from neutral complex 1 in the presence of ethylene
was ascertained by DFT calculation (Figure 2).11 In conse-
quence, the cationic complex is suggested to possess two avail-
able cis-located sites needed for efficient olefin polymerization.
Subsequently, complexes 1 and 2 were investigated as eth-
ylene polymerization catalysts using MAO as a cocatalyst at 25
°C under ethylene at atmospheric pressure (Table 1, entries 1
and 2).12 Complex 1 furnished an activity of 6000 kg-poly-
mer·mol-Ti–1·h–1. As far as we are aware, this is one of the
highest activity values displayed by homogeneous titanium
complexes with no Cp ligand(s) under the same polymerization
conditions. The viscosity-average molecular weight (Mv) value
of the polymer thus obtained was 7.5 × 104.13 Interestingly,
complex 2, having a cyclohexyl group instead of the phenyl
group, displayed 14100 kg-polymer·mol-Ti–1·h–1 of activity
with a very high Mv value of 260.1 × 104. This activity value,
14100 kg-polymer·mol-Ti–1·h–1, is comparable to that of
Cp2TiCl2 (16700 kg-polymer·mol-Ti–1·h–1 ).
5
6
Alternatively, using Ph3C+B–(C6F5)4/iBu3Al as a cocatalyst
in the place of MAO, these complexes provided polyethylene
which did not dissolve wholly in decalin solvent under the
intrinsic viscosity measurement conditions, suggesting that the
polyethylene thus obtained possesses exceptionally high molec-
ular weight (Table 1, entries 4 and 5).12,13
7
8
9
V. C. Gibson, P. J. Maddox, C. Newton, C. Redshaw, G. A. Solan,
A. J. P. White, and D. J. Williams, Chem. Commun., 1998, 1651.
S. Matsui, M. Nitabaru, Y. Yoshida, M. Mitani, and T. Fujita, EP
Patent 1008595 (2000); Chem. Abstr., 133, 43969 (2000).
Complex 1: 1H-NMR (270 MHz, CDCl3, 25 °C, TMS): δ =
6.0–7.9 (m, 6H(pyrrole ring)+10H(benzene ring); aromatic-H),
7.80 (s, 2H; CH=N). Anal. Found: C, 58.29; H, 3.95; N, 12.62%.
Calcd for C22H18N4TiCl2: C, 57.80; H, 3.97; N, 12.25%. FD-mass:
m/z: 456 (M+). Crystal data for complex 1: Formula
C22H18N4Cl2Ti, FW = 457.22, monoclinic, P21/n, a = 11.606(2), b
= 14.200(2), c = 14.294(2) Å, β = 113.59(1)°, V = 2158.9(6) Å3, Z
= 4, Dcalcd = 1.407 g/cm3, T = 296 K, 5175 unique reflections,
R(Rw) = 0.031(0.029). Complex 2: 1H-NMR (270 MHz, CDCl3,
25 °C, TMS): δ = 0.7–2.7 (m, 22H; cyclohexyl-H), 6.2–7.9 (m, 6H;
aromatic-H), 8.00 (s, 2H; CH=N). Anal. Found: C, 56.79; H,
6.71; N, 12.12%. Calcd for C22H30N4TiCl2: C, 56.31; H, 6.44; N,
11.94%. FD-mass: m/z: 468 (M+). Crystal data for complex 2:
Formula C22H18N4TiCl2, FW = 469.31, monoclinic, P21/c, a =
14.064(9), b = 11.446(2), c = 14.354(2) Å, β = 92.06(3), V =
2309(1) Å3, Z = 4, Dcalcd = 1.350 g/cm3, T = 150 K, 4699 unique
reflections, R1 = 0.058 (for 4496 data with I > 2σ(I)), R(Rw) =
0.114(0.166). Single crystals of the titanium complexes 1 or 2 suit-
able for X-ray analysis were grown from a saturated hexane /
CH2Cl2 solutions.
10 I. Kim, Y. Nishihara, R. F. Jordan, R. D. Rogers, A. L. Rheingold,
and G. P. A.Yap, Organometallics, 16, 3314 (1997).
11 DFT calculation has been widely used for structural determination
of transition metal complexes, cf.; L. Deng, T. Zieglar, T. K. Woo,
P. Margl, and L. Fan, Organometallics, 17, 3240 (1998). All cal-
culations were performed using gradient corrected density func-
tional method BLYP, by means of the Amsterdam Density
Functional (ADF) program. We used the electronic configuration
of molecular system described by a triple -ζ basis set on the metal
center. A double -ζ basis set was used for ethylene as a monomer
and methyl group as a model of polymer chain. For the other
atoms, a single -ζ basis set was used.
In summary, two new titanium complexes having two
pyrolide-imine ligands were introduced. These complexes
exhibited high ethylene polymerization activity using MAO or
Ph3C+B–(C6F5)4/iBu3Al as cocatalysts. These results together
with our previous reports suggest that both titanium and zirco-
nium complexes bearing multidentate and non-symmetric lig-
ands have high potential as highly active new olefin polymer-
ization catalysts.4,6a
12 General polymerization procedure: Flow of ethylene gas was
charged into toluene with vigorous stirring. To this solution, MAO
and a toluene solution of a complex was added. In the case of
We thank Dr. T. Oshiki, Okayama University, for X-ray
measurement and analysis.
i
Ph3C+B–(C6F5)4/iBu3Al cocatalyst system, Bu3Al, complex solu-
tion, Ph3C+B–(C6F5)4 were added, in this order, to the solution.
13 Mv values were calculated from the following equation, [η] = 6.2
× 10–4Mv0.7; R. Chiang, J. Polymer Sci., 36, 91 (1959). Intrinsic
viscosity [η] was measured in decalin at 135 °C using an
Ubbelohde viscometer. Preparation of intrinsic viscosity measure-
ment solution; 25 mg of polyethylene was dissolved into 25 mL of
decalin at 135 °C.
References and Notes
1
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and M. Brookhart, Chem. Rev., 100, 1169 (2000).
2