Titanium complexes with novel triaryl-substituted phosphinimide ligands: Synthesis, structure and ethylene polymerization behavior

Article abstract of DOI:10.1016/j.jorganchem.2005.11.048

A series of titanium phosphinimide complexes [Ph₂P(2-RO-C ₆H₄)]₂TiCl₂ (7, R = CH₃; 8, R = CHMe₂) and [PhP(2-Me₂CHO-C₆H ₄)][THF]TiCl₃ (

Full text of DOI:10.1016/j.jorganchem.2005.11.048

Journal of Organometallic Chemistry 691 (2006) 1154–1158
www.elsevier.com/locate/jorganchem
Titanium complexes with novel triaryl-substituted
phosphinimide ligands: Synthesis, structure and ethylene
polymerization behavior
a,
Changhe Qi a,b, Suobo Zhang
*
a
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences,
5625 Renmin Street, Changchun 130022, China
b
Graduate School of the Chinese Academy of Sciences, China
Received 18 June 2005; received in revised form 10 November 2005; accepted 22 November 2005
Available online 28 December 2005
Abstract
A series of titanium phosphinimide complexes [Ph2P(2-RO-C6H4)]2TiCl2 (7, R = CH3; 8, R = CHMe2) and [PhP(2-Me2CHO–
C6H4)][THF]TiCl3 (9) have been prepared by reaction of TiCl4 with the corresponding phosphinimines under dehalosilylation. The struc-
ture of complex 9 has been determined by X-ray crystallography, and a solvent molecule THF was found to be coordinated with the
central metal and the Ti–O bond was consistent with the normal Ti–O (donor) bond length. The complexes 7 and 8 displayed inactive
to ethylene polymerization, and the complex 9 displayed moderate activity in the presence of modified methylaluminoxane (MMAO)
or i-Bu3Al/Ph3CB(C6F5)4, and this should be partly attributed to coordination of THF with titanium and the steric effect of two
iso-propoxyl. And catalytic activity up to 32.2 kg-PE/(mol-Ti h bar) was observed.
ꢀ 2005 Elsevier B.V. All rights reserved.
Keywords: Complex; Titanium; Phosphinimine; Ethylene polymerization
1. Introduction
25 ꢁC) and commercially relevant (103 bar and 160 ꢁC)
polymerization conditions [7]. They thought that bulky
phosphinimide ligands could provide the metal environ-
ments that sterically and electronically mimic metallocenes.
Importantly, the phosphinimines were easily prepared by
simple azide oxidation of phosphine ligands, and the high
oxidate-state P-based ligands were expected to be thermally
stable. Most of phosphinimines they used were based on
alkylphosphines [8].
There were many reports of titanium complexes based
on triphenylphosphinimine ligands [9], however, few of
them were used as olefin polymerization catalysts. Herein,
we would like to report the synthesis, structure, and ethyl-
ene polymerization of titanium phosphinimide complexes
bearing alkyloxyl substituted triphenylphosphines. We
hope that these ligands could also function well as analogy
of cyclopentadienyl ligands and o-alkoxy substituents
could protect the phosphinimide-N atom from the attack
of lewis acid activators by steric effect effectively.
The search for non-metallocene olefin polymerization
catalysts has been the subject of a number of research
groups around the world for many years [1]. There were
many reports for early and late transition metal complexes
based on new or known ligands, such as bidentate diamides
[2], phenoxy-imines [3], pyrrolide-imines [4], phenoxy-
ethers [5], and tridentate [6] [Nꢀ, N, Nꢀ], [Nꢀ, O, Nꢀ],
[Oꢀ, N, P] chelate ligands.
More recently, Stephan and coworkers have reported a
series of titanium and zirconium phosphinimide complexes
and most of them showed to be excellent olefin polymeriza-
tion catalysts under both laboratory screening (1 atm. and
*
Corresponding author. Tel.: +86 431 5262347.
E-mail addresses: changheq@ciac.jl.cn (C. Qi), sbzhang@ciac.jl.cn
(S. Zhang).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.11.048

C. Qi, S. Zhang / Journal of Organometallic Chemistry 691 (2006) 1154–1158
1155
2. Results and discussion
2.1. Synthesis and characterization of complexes
The synthesis of the ligands and complexes was outlined
in Scheme 1. The substituted triphenylphosphines 1–3 were
readily prepared according to literature [10]. Oxidation of
the 1–3 with Me3SiN3 resulted in the evolution of N2.
The pure phosphinimines 4–6 could be obtained after dis-
tillation in yield 57–79%. Treatment of 4–6 with TiCl4 (at
the molar ratio 2:1 (4, 5) or 1:1 (6)) in THF under dehalo-
silylation generated titanium phosphinimide complexes 7–9
in yield 86–92% (the attempt to prepare the dichloride tita-
nium complex based on ligand 6 was failed at the ratio 2:1
and only little 9 could be obtained).
All the new compounds 4–9 were characterized by
NMR, element analysis and mass analysis. The single crys-
tals of complex 9 suitable for X-ray diffraction study were
grown from THF/hexane under argon atmosphere at
ꢀ20 ꢁC. The ORTEP diagram was shown in Fig. 1. The
crystal data was summarized in Table 1 and selected bond
lengths and angles were summarized in Table 2.
Fig. 1. ORTEP drawings of complex 9. Thermal ellipsoids at the 30%
level are shown. The hydrogen atoms are omitted for clarity.
The Ti–N bond distance of complex 9 was found to be
˚
1.716(6) A and showed the double bond characters. It
MMAO, and only trace of polymers was obtained for
complexes 7 and 8. While, the complex 9 displayed moder-
ate activity (23.2 kg-PE/(mol-Ti h bar), Al/Ti = 2000/1,
7.6 lmol, 15 min) under atmospheric pressure at room
temperature.
It was the electron-withdrawing of phenyl on phosphin-
imines that resulted in the inactivity of complexes 7 and 8
(the complex (t-Bu3PN)2TiCl2 also showed poor activity
in the presence of MAO at atmospheric pressure but no
exact data was reported [7a]), and it was consistent with
the computational results of Stephan and coworkers [11],
which indicated that the use of electron-donating substitu-
ents would result in significantly smaller ion pair separation
energy, thus enhancing catalytic activity. So, the use of
electron-withdrawing substituents should correspondingly
was found that there was a solvent THF coordinating with
the central metal and it was consistent with NMR data.
Ti–O distance (2.156(5) A) was consistent with the normal
˚
˚
Ti–O (donor) bond length (ꢁ2.15–2.20 A) [6b]. Therefore,
the coordination of the oxygen in THF with titanium
appeared to be capable of stabilizing the incipient electro-
philic titanium cation to a significant degree. The P–N–Ti
angle (175.3(4)ꢁ) was essentially linear and consistent with
similar complexes in the literature.
2.2. Ethylene polymerization
Preliminary evaluation of compounds 7–9 as ethylene
polymerization catalysts was performed in the presence of
NSiMe3
PPh2
RO
OR
P N TiCl2
RO
PPh2
Me3SiN3
-N2
TiCl4
Ph2
2
4-5
7-8
1-2
O
O
O
NSiMe3
PPh
Ph
Me3SiN3
-N2
TiCl4
P
N TiCl3
O
PPh
2
2
2
6
9
3
1, 4, 7: R = CH3;
2, 5, 8: R = CH(CH3)2
Scheme 1. The synthesis of ligands and complexes.

1156
C. Qi, S. Zhang / Journal of Organometallic Chemistry 691 (2006) 1154–1158
Table 1
Table 3
a
Crystallographic data structure refinements of 9
Polymerization of ethylene by the complex 9/i-Bu3Al/Ph3CB(C6F5)4
b
Empirical formula
Formula mass
Crystal size (mm)
Crystal system
Space group
C28H35Cl3NO3PTi
618.79
0.30 · 0.23 · 0.10
Triclinic
Run
Al/Ti/TB
Yield (mg)
Activity
Mv
1
2
3
4
5
a
100/1/1
100/1/2
100/1/3
200/1/2
400/1/2
15.3
25.5
24.6
19.5
17.6
19.3
32.2
31.1
24.6
22.2
–
131.5
172.3
–
ꢀ
P1
˚
a (A)
9.8910(16)
10.0026(16)
16.189(16)
79.108(4)
86.353(4)
82.694
1558.8(4)
–
˚
b (A)
˚
Polymerization condition: 1 atm pressure of ethylene; toluene 50 ml;
10 min; complex 4.75 lmol; Al, i-Bu3Al; TB, trityl tetrakis(penta-
fluorphenyl)borate.
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
b
Activity in kg-PE/(mol-Ti h bar).
3
˚
V (A )
Z
2
Density (calcd.) (Mg cmꢀ3
)
1.318
0.611
The attempts to prepare other similar bulky and elec-
tron-donating ortho-substituted phosphinimines and their
complexes are underway.
Absorption coefficient (mmꢀ1
)
F(000)
644
2.08–25.04
8146
h Range for data collected (ꢁ)
Reflection collected
Data/restraints/parameters
Independent reflections
Final R indices [I > 2r(I)]
R indices (all data)
5386/0/338
3. Experimental
5386 (Rint = 0.0764)
R1 = 0.0825, wR2 = 0.1456
R1 = 0.2196, wR2 = 0.1957
Semi-empirical from equivalents
0.961
3.1. General
Absorption correction
Goodness-of-fit on F2
Largest difference peak
All manipulations were done under an atmosphere of
dry argon employing standard Schlenk and cannula tech-
nique. Solvents were distilled under argon over sodium-
benzophenone (THF, ether, toluene, n-hexane). NMR data
of complexes were obtained on a Varian Unity 300 MHz
spectrometer at ambient temperature, C6D6 or d6-DMSO
as solvent. Mass spectra were obtained using electron
impact (EIMS) and LDI-1700 (Linear Scientific Inc.). Ele-
mental analyses were recorded on an elemental Vario EL
spectrometer. The substituted triphenylphosphines 1–3
were synthesized according to literatures [9].
0.475 and ꢀ0.323
ꢀ3
˚
and hole (e A
)
Table 2
˚
Selected bond distances (A) and angles (ꢁ) for complex 9
˚
Bond lengths (A)
Ti–N
P–N
Ti–Cl(1)
Ti–Cl(2)
Ti–Cl(3)
Ti–O(3)
1.716(6)
1.617(6)
2.307(3)
2.284(2)
2.302(2)
2.156(5)
3.2. Synthesis of ligands
Bond angles (ꢁ)
P–N–Ti
N–Ti–O(3)
175.3(4)
91.8(2)
3.2.1. Synthesis of ligand 4
Me3SiN3 (2.17 g, 18.9 mmol) was injected into the com-
pound (2-methoxyphenyl)diphenylphosphine 1 and stirred
10 h at 100 ꢁC. Fractional distillation of the residue gave
the product as a viscous liquid; yield 4.6 g, 71%, b.p. ca.
195 ꢁC (0.3 mmHg). Anal. Calcd. for C22H26NOPSi: C,
69.65; H, 6.86; N, 3.69; Found: C, 69.73; H, 6.81; N,
3.66%. 1H NMR (300 MHz, DMSO): d: 7.56–7.45 (m,
6H, Ar-H); 7.42–7.34 (m, 6H, Ar-H); 7.01–6.99 (m, 6H,
Ar-H); 3.99 (s, 3H, OCH3); ꢀ0.25 (s, 9H, –Si(CH3)3).
MS: m/z = 379 (M+).
Cl(1)–Ti–Cl(2)
Cl(1)–Ti–Cl(3)
Cl(2)–Ti–Cl(3)
92.35(10)
92.23(9)
132.88(11)
decrease catalytic activity. Compared with complexes 7–8,
there were two iso-propoxyl at the ortho-position of phos-
phorus in one ligand as electron-donor in complex 9.
Mainly, they could protect the phosphinimide-N atom from
the attack of lewis acid activators by steric effect. And the
coordination of THF with titanium will also satisfy to a
certain extent the electron requirement of titanium.
Activated by i-Bu3Al/Ph3CB(C6F5)4, the complex 9 was
further investigated for ethylene polymerization, and the
results were collected in Table 3. Moderate activities, but
slightly higher than that in the case of MMAO, were
observed at different ratio of Al/Ti and B/Ti. Molecular
weight was measured by Ubbelohde viscometer on
ꢁ0.08% (w/v) polymer solution in decalin at 135 ꢁC. The
following equation was used to estimate the molecular
weight: g ¼ 6:2 ꢂ 10ꢀ4 Mg0:7 [12].
3.2.2. Synthesis of ligand 5
The synthesis of 5 was carried out by the same proce-
dure as that for ligand 4 except that compound (2-iso-prop-
oxyphenyl)diphenylphosphine 2 was used in place of
compound 1. Yield: 79%. b.p. ca. 203 ꢁC (0.3 mmHg).
Anal. Calcd. for C24H30NOPSi: C, 70.76; H, 7.37; N,
3.44; Found: C, 70.84; H, 7.29; N, 3.24%. 1H NMR
(300 MHz, DMSO): d: 7.67–7.62 (m, 1H, Ar-H); 7.60–
7.57 (m, 2H, Ar-H); 7.56–7.53 (m, 2H, Ar-H); 7.44–7.33
(m, 7H, Ar-H); 6.98–6.90 (m, 2H, Ar-H); 4.45 (m, 1H,

C. Qi, S. Zhang / Journal of Organometallic Chemistry 691 (2006) 1154–1158
1157
OCH–); 0.72 (d, 6H, C(CH3)2); ꢀ0.23 (s, 9H, –Si(CH3)3).
MS: m/z = 407 (M+).
(50 ml) was added after the reactor was flammable dried.
Then, MMAO (2 mol/L) was injected, the toluene solution
of catalysts was added to initiate the polymerization. In the
case of i-Bu3Al/Ph3CB(C6F5)4, toluene solution of i-Bu3Al
was added first, toluene solution of Ph3CB(C6F5)4 was
added to initiate polymerization after the addition of cata-
lysts solution. After the desired time, the polymerization
was stopped by quenching with 200 ml of aqueous HCl/
ethanol. The polymer was collected by filtration, washed
subsequently with HCl solution, ethanol, water, and dried
at 50 ꢁC to a constant weight.
3.2.3. Synthesis of ligand 6
The synthesis of 6 was carried out by the same procedure
as that for ligand 4 except that compound (2-di-iso-prop-
oxyphenyl)phenylphosphine 3 was used in place of com-
pound 1. Yield: 57%. b.p. ca. 211 ꢁC (0.3 mmHg). Anal.
Calcd. for C27H36NO2PSi: C, 69.68; H, 7.74; N, 3.01;
1
Found: C, 70.05; H, 7.66; N, 3.12%. H NMR (300 MHz,
DMSO): d: 7.90–7.83 (m, 1H, Ar-H); 7.80–7.74 (m, 1H,
Ar-H); 7.40–7.31 (m, 7H, Ar-H); 6.92–6.83 (m, 4H, Ar-
H); 4.46–4.37 (m, 2H, OCH–); 0.75–0.69 (d, 12H,
C(CH3)2); ꢀ0.23 (s, 9H, –Si(CH3)3). MS: m/z = 465 (M+).
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic Data
Center, CCDC no. 254442 for 9. 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; e-mail: deposit@ccdc.cam.ac.uk or www: http://
ccdc.cam.ac.uk).
3.3. Synthesis of complexes
3.3.1. Synthesis of complex 7
Twenty milliliter of THF solution of ligand 4 (2.2 g,
5.8 mmol) was added via a cannula to a 20 ml Et2O solu-
tion of TiCl4 (0.55 g, 2.9 mmol) at 0 ꢁC. The solution was
allowed to warm to room temperature and stirred for
16 h. Then, the solvent was removed in vaccuo to give a
yellow solid. THF (15 ml) and n-hexane (40 ml) were added
one by one. The product was crystallized at ꢀ20 ꢁC as yel-
Acknowledgements
The authors are grateful for financial supported by the
National Natural Science Foundation of China and SINO-
PEC (No. 20334030).
1
low solid. Yield: 1.82 g, 86%. H NMR (300 MHz, C6D6):
d: 7.82–7.81 (m, 10H, Ar-H); 7.27–7.07 (m, 18H, Ar-H);
3.11 (s, 6H, OCH3). Anal. Calcd. for C38H34Cl2N2O2P2Ti:
C, 62.38; H, 4.65; N, 3.83; Found: C, 63.19; H, 4.62; N,
3.80%. MS: m/z = 731 (M+).
References
[1] (a) G.P. Britovsek, V.C. Gibson, D.F. Wass, Angew. Chem. Int. Ed.
38 (1999) 428;
3.3.2. Synthesis of complex 8
(b) V.C. Gibson, S.K. Spitzmesser, Chem. Rev. 103 (2003) 283.
[2] (a) J.D. Scollard, D.H. McConville, J. Am. Chem. Soc. 118 (1996)
10008;
(b) A.D. Horton, K.L. von Hebel, J. de With, Macromol. Symp. 173
(2001) 123.
[3] (a) S. Matsui, M. Mitani, J. Saito, Y. Tohi, H. Makio, H. Tanaka,
T. Fujita, Chem. Lett. (1999) 1263;
(b) M. Mitani, R. Furuyama, J. Mohri, J. Saito, S. Ishii, H. Terao,
N. Kashiwa, T. Fujita, J. Am. Chem. Soc. 124 (2002) 7888;
(c) M. Mitani, R. Furuyama, J. Mohri, J. Saito, S. Ishii, H. Terao, T.
Nakano, H. Tanaka, T. Fujita, J. Am. Chem. Soc. 125 (2003) 4293.
[4] Y. Yoshida, S. Matsui, Y. Takagi, M. Mitani, M. Nitabaru, T.
Nakano, H. Tanaka, T. Fujita, Chem. Lett. (2000) 1270.
[5] Y. Suzuki, Y. Inoue, H. Tanaka, T. Fujita, Macromol. Rapid
Commun. 25 (2004) 493.
The synthesis of 8 was carried out by the same proce-
dure as that for ligand 7 except that ligand 5 was used in
place of ligand 4. Yield: 89%. 1H NMR (300 MHz,
C6D6): d: 7.44–7.43 (m, 10H, Ar-H); 6.86–6.68 (m, 14H,
Ar-H); 6.35–6.33 (m, 2H, Ar-H); 5.99–5.97 (m, 2H, Ar-
H); 3.58 (m, 2H, OCH–); 0.37–0.36 (d, 12H, CMe2). Anal.
Calcd. for C42H42Cl2N2O2P2Ti: C, 64.12; H, 5.34; N, 3.56;
Found: C, 64.50; H, 5.29; N, 3.59%. MS: m/z = 786 (M+).
3.3.3. Synthesis of complex 9
The synthesis of 9 was carried out by the same proce-
dure as that for ligand 7 except that ligand 6 was used in
place of ligand 4. Yield: 92%. 1H NMR (300 MHz,
C6D6): d: 7.96 (m, 2H, Ar-H); 7.73–7.65 (m, 5H, Ar-H);
7.43 (m, 1H, Ar-H); 7.25 (m, 1H, Ar-H); 7.18 (m, 2H,
Ar-H); 7.00–6.95 (m, 2H, Ar-H); 4.60–4.56 (m, 2H,
OCH–); 3.84 (b, 4H, O–CH2THF); 1.91 (b, 4H, C–CH2THF);
1.03–0.97 (d, 12H, CMe2). Anal. Calcd. for C28H35-
Cl3NO3PTi: C, 54.37; H, 5.66; N, 2.26; Found: C, 54.62;
H, 5.57; N, 2.29%. MS: m/z = 618 (M+).
´
[6] (a) F. Guerin, D.H. McConville, J.J. Vittal, Organometallics 15
(1996) 5586;
(b) R. Baumann, W.M. Davis, R.R. Schrock, J. Am. Chem. Soc. 119
(1997) 3830;
(c) W.-Q. Hu, X.-L. Sun, C. Wang, Y. Gao, Y. Tang, L.-P. Shi, W.
Xia, J. Sun, H.-L. Dai, X.-Q. Li, X.-L. Yao, X.-R. Wang, Organo-
metallics 23 (2004) 1684.
[7] (a) D.W. Stephan, F. Gue´rin, R.E.v.H. Spence, L. Koch, X. Gao,
S.J. Brown, J.W. Swabey, Q. Wang, W. Xu, P. Zoricak, D.G.
Harrison, Organometallics 18 (1999) 2046;
(b) C. Carraz, D.W. Stephan, Organometallics 19 (2000) 3791;
3.4. Typical polymerization procedure
´
(c) D.W. Stephan, J.C. Stewart, F. Guerin, S. Courtenay, J. Kickham,
E. Hollink, C. Beddie, A. Hoskin, T. Graham, P. Wei, R.E.v.H.
Spence, W. Xu, L. Koch, X. Gao, D.G. Harrison, Organometallics
22 (2003) 1937.
Ethylene polymerization was carried out in a 250 ml
glass reactor equipped with a mechanical stirrer. Toluene

1158
C. Qi, S. Zhang / Journal of Organometallic Chemistry 691 (2006) 1154–1158
[8] (a) D.W. Stephan, Macromol. Symp. 173 (2001) 105;
(b) D.W. Stephan, Organometallics 24 (2005) 2548;
(e) M. Sotoodeh, I. Leichtweis, H.W. Roesky, M. Noltmeyer, H.-G.
Schmidt, Chem. Ber. 126 (1993) 913.
´
(c) F. Guerin, J.C. Stewart, C. Beddie, D.W. Stephan, Organomet-
[10] (a) J. Blin, P. Braunstein, J. Fischer, G. Kickelbick, M. Knorr,
X. Morise, T. Wirth, J. Chem. Soc., Dalton Trans. (1999)
2159;
allics 19 (2000) 2994.
[9] (a) I.A. Latham, G.J. Leigh, G. Huttner, I. Jibril, J. Chem. Soc.,
Dalton Trans. (1986) 377;
(b) H.D. Empsall, B.L. Shaw, B.L. Turtle, J. Chem. Soc.
Dalton. (1976) 1500;
(b) T. Rubenstahl, D. Wolff von Gudenberg, F. Weller, K. Dehnicke,
¨
H. Goesmann, Z. Naturforsch. B 49 (1994) 15;
(c) J.-S. Li, M. Stahl, N. Faza, W. Massa, K. Dehnicke, Z. Anorg.
Allg. Chem. 623 (1997) 1035;
(c) A. van Zon, G.J. Torny, J.H.G. Frijns, Recl. Trav. Chim.
Pays-Bas 102 (1983) 326.
[11] C. Beddie, E. Hollink, P. Wei, J. Gauld, D.W. Stephan, Organomet-
allics 23 (2004) 5240.
(d) T. Rubenstahl, F. Weller, S. Wocadlo, W. Massa, K. Dehnicke,
¨
Z. Anorg. Allg. Chem. 621 (1995) 953;
[12] R. Chiang, J. Polym. Sci. 28 (1957) 235.