Ethylene polymerization and ring-opening metathesis polymerization of norbornene catalyzed by (arylimido)(aryloxy)vanadium(V) complexes of the type, V(NAr)(OAr′)X2 (X = Cl, CH2Ph)

Article abstract of DOI:10.1246/cl.2001.36

VCl₂(N-2,6-Me₂C₆H₃)(O-2,6 ⁱPr₂C₆H₃) - methylaluminoxane catalyst has exhibited remarkable catalytic activity for ethylene polymerization. High molecular weight ring-op

Full text of DOI:10.1246/cl.2001.36

36
Chemistry Letters 2001
Ethylene Polymerization and Ring-Opening Metathesis Polymerization of Norbornene Catalyzed
by (Arylimido)(aryloxy)vanadium(V) Complexes of the Type,V(NAr)(OAr')X2 (X = Cl, CH2Ph)
Kotohiro Nomura,* Asami Sagara, and Yukio Imanishi
Graduate School of Materials Science, Nara Institute of Science and Technology (NAIST),
8916-5 Takayama, Ikoma, Nara 630-0101
(Received October 11, 2000; CL-000924)
VCl2(N-2,6-Me2C6H3)(O-2,6-iPr2C6H3) - methylalumi-
noxane catalyst has exhibited remarkable catalytic activity for
ethylene polymerization. High molecular weight ring-opened
poly(norbornene) has been prepared in the presence of
V(CH2Ph)2(N-2,6-Me2C6H3)(O-2,6-iPr2C6H3).
Olefin polymerization by homogeneous transition metal
catalysis attracts particular attention not only in the field of
organometallic chemistry, but also in the field of polymer
chemistry.1 Although a lot of examples have been well-known
concerning the effective catalysts with group 4B transition
metal catalysts, examples with vanadium complexes have been
limited2,3 despite the fact that classical Ziegler–Natta vanadium
catalyst systems have displayed a number of interesting charac-
teristics4 such as synthesis of high molecular weight polymers
with narrow polydispersity,5 synthesis of ethylene/α-olefin
copolymer with high α-olefin content,6 and others.7 We thus
decided to extend our chemistry to find a new-type of vanadium
catalyst for olefin polymerization.
We focused (arylimido)vanadium(V) complex as the start-
ing compounds, because synthesis of vanadium complexes with
various arylimido ligand have already been established by sev-
eral researchers,8 and also because this ligand moiety should be
relatively stable at high temperature.8c Moreover, we also
focused to synthesize 14e vanadium(V) complex which should
be the same electron number of our original half-metallocene
type titanium catalyst.9 In this paper, we wish to introduce our
preliminary results concerning olefin polymerization by
(arylimido)(aryloxy)vanadium(V) complexes.
iPr2C6H3 (1a), O-2,6-tBu2-4-MeC6H2 (1b)] have been prepared
in high yields from VCl3(NAr) by treating with 1 equivalent of
the corresponding phenol in hexane (Scheme 1).10 These com-
plexes have also been prepared by adding the corresponding
lithium phenoxide in Et2O. The products isolated were deep
1
purple microcrystals, and could be identified by H, 13C NMR
and repeated elemental analysis runs.10
Importantly, VCl2(N-2,6-Me2C6H3)(O-2,6-iPr2C6H3) (1a)
exhibited significant catalytic activity for ethylene polymeriza-
tion in the presence of d-MAO (methylaluminoxane, white
solid) which was prepared by removing toluene and excess
amount of AlMe3 from commercially available MAO (PMAO-
S, Tosoh Akzo Co.), and the activity increased at higher reac-
tion temperature (runs 1–3, Table 1). In addition, the resultant
polymer was linear, which was confirmed by NMR spec-
troscopy, and has exceptionally high molecular weight with
unimodal molecular weight distribution, and the polymerization
results were reproducible under these conditions. The lower
activity was observed if MMAO was used as cocatalyast in
place of d-MAO. The activity by 1b was lower than that by 1a,
suggesting that the steric bulk of the aryloxy ligand affects the
(Arylimido)(aryloxy)vanadium complexes of the type,
VCl2(NAr)(OAr') [NAr = N-2,6-Me2C6H3, OAr' = O-2,6-
Copyright © 2001 The Chemical Society of Japan

Chemistry Letters 2001
37
Doughty, J. M. Marandon, and G. A. Skinner, Eur. Polym. J., 10,
481 (1974).
For example (synthesis of syndiotactic polypropylene), Y. Doi,
N. Tokuhiro, M. Nunomura, H. Miyake, S. Suuki, and K. Soga,
in “Transition Metals and Organometallic as Catalysts for Olefin
Polymerization,” ed. by W. Kaminsky and H. Sinn, Springer-
Verlag, Berlin (1988), p. 379.
For example, A. Zambelli, A. Proto, and P. Longo, in “Ziegler
Catalysts,” ed. by G. Fink, R. Mulhaupt, and K. H. Brintzinger,
Springer-Verlag, Berlin (1995), p. 217.
a) D. D. Devore, J. D. Lichtenhan, F. Takusagawa, and E. A.
Maata, J. Am. Chem. Soc., 109, 7408 (1987). b) J. -K. F. Buijink,
J. H. Teubin, H. Kooijman, and A. L. Spek, Organometallics, 13,
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Inorg. Chem., 35, 3695 (1996).
activity. We assume that the reason for the higher activity than
those previously reported using a series of (arylimido)vanadi-
um(V) complexes2b,c would be due to the low coordinate (14e)
vanadium species as the starting catalyst precursor.
Attempt to isolate dibenzyl complex from 1a by treating
with PhCH2MgCl was not successful, probably due to the diffi-
culty for isolating from the reaction mixture. However, the
desired complex V(CH2Ph)2(N-2,6-Me2C6H3)(O-2,6-iPr2C6H3)
(2) could be synthesized from its tribenzyl analogue,
V(CH2Ph)3(N-2,6-Me2C6H3),11 by treating with 1 equivalent of
2,6-iPr2C6H3OH in CH2Cl2.12
It should be noted that ring-opened poly(norbornene) could
be isolated if norbornene and 2 were dissolved in toluene.13
This is, as far as we know, the first example of the ring-opening
metathesis polymerization (ROMP) initiated by the vanadium
complex without cocatalyst. Moreover, this is also the rare
example affording exceptionally high molecular weight poly-
mer with unimodal molecular weight distribution (Mw = 4.69 ×
106, Mw/Mn = 1.93).14 Since the polymerization would proceed
via metathesis mechanism, we assume that the vanadium-
alkylidene complex would be the active species in this cataly-
sis.15
We are now exploring the effect of substituents for the
activity in ethylene polymerization, and attempting isolation of
vanadium–alkylidene complex which should be the proposed
active species for the ROMP. These results will be introduced
in the future.
6
7
8
9
For example, a) K. Nomura, N. Naga, M. Miki, K. Yanagi, and
A. Imai, Organometallics, 17, 2152 (1998). b) K. Nomura, K.
Oya, T. Komatsu, and Y. Imanishi, Macromolecules, 33, 3187
(2000).
10 General experimental procedure for synthesis of 1a: Into a n-
hexane solution (30 mL) containing V(N-2,6-Me2C6H3)Cl3 (1.30
g, 4.70 mmol), 2,6-iPr2C6H3OH (838 mg, 4.70 mmol) was added
dropwisely at –30 °C, and the reaction mixture was warmed
slowly to room temperature, and then the mixture was stirred for
10 h. The solvent was removed in vacuo, and the resultant deep
brown tan residue was layered by n-hexane (ca. 5 mL) at –30 °C.
The chilled solution gave deep brown solid, which was washed
quickly with small amount of cold hexane and dried in vacuo.
Yield 1.82 g (93%). 1H NMR (CDCl3): δ 1.13 (d, 12H,
(CH3)2CH–, J = 6.8 Hz), 2.38 (s, 6H, CH3), 3.24 (m, 2H,
Me2CH–), 6.82 (m, 3H), 7.10 (m, 3H) . 13C NMR (CDCl3): δ
18.3, 23.2, 27.1, 123.3, 126.2, 127.3, 129.6, 136.2, 138.9, 166.5.
Anal. Calcd for C20H26Cl2NOV: C, 57.43; H, 6.27; N, 3.35.
Found (1): C, 57.46; H, 6.42; N, 3.22%. Found (2): C, 57.42, H,
6.40, N, 3.28%. For 1b, Yield 94%. 1H NMR (CDCl3): δ 0.97
(s, 18H), 1.93 (s, 3H), 2.07 (s, 6H), 6.42 (m, 3H), 6.64 (s, 1H),
6.82 (s, 1H). 13C NMR (CDCl3): δ 21.5, 22.7, 31.9, 35.5, 125.5,
126.0, 127.3, 129.9, 134.4, 139.0, 139.1, 168.6 . Anal. Calcd for
References and Notes
1
For example (Review), a) H. H. Brintzinger, D. Fischer, R.
Mülhaupt, B. Rieger, and R. M. Waymouth, Angew. Chem., Int.
Ed. Engl., 34, 1143 (1995). b) W. Kaminsky, Macromol. Chem.
Phys., 197, 3903 (1996). c) W. Kaminsky and M. Arndt, Adv.
Polym. Sci., 127, 143 (1997). d) J. Suhm, J. Heinemann, C.
Wörner, P. Müller, F. Stricker, J. Kressler, J. Okuda, and R.
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38, 429 (1999).
C
23H32Cl2NOV: C, 60.01; H, 7.01; N, 3.04%. Found(1): C,
59.86; H, 7.13; N, 2.80%. Found(2): C, 60.05; H, 7.24; N,
2.91%.
11 This complex was prepared according to the analogous procedure
for synthesis of V(CH2Ph)3(N-2,6-iPr2C6H3), V. J. Murphy and
H. Turner, Organometallics, 16, 2495 (1997).
12 Experimental procedure: Into a cold CH2Cl2 solution (25 mL, –30
°C) of V(CH2Ph)(N-2,6-Me2C6H3) (1.0 g, 2.25 mmol), 2,6-diiso-
propylphenol was added in several portions and the mixture was
stirred for 40 h at room temperature. The reaction mixture was
filtered through Celite pad, and the solvent was removed in
vacuo, and the resultant solid was dissolved in small amount of
hexane. The chilled solution gave deep brown microcrystals.
2
3
a) F. J. Feher and R. L. Blanski, Organometallics, 12, 958 (1993).
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1
Yield 75%. For 2, H NMR(CDCl3): δ 1.32 (d, 12H), 2.97 (d,
10H), 3.20 (m, 2H), 7.23 (m, 16H). 13C NMR (CDCl3): δ 22.7,
27.1, 37.8, 37.9, 77.2, 120.6, 123.4, 125.9, 128.3, 128.4, 133.6,
141.8, 150.0.
Catalytic activity for ethylene polymerization in the previous
reports, 14 kg-PE/mol-V·h (ethylene 1 atm, in toluene, MAO
cocatalyst, r.t. 105 min, Mw = 4.7 × 104, Mw/Mn = 3.0) by
Tp*V(N-2,6-iPr2C6H3)Cl2 [Tp* = hydrotris(3,5-dimethylpyra-
zolyl)borato],2b 27 kg-PE/mol-V·h (ethylene 1 atm, in toluene,
MAO cocatalyst, 25 °C, 1 h) by CpV(N-4-MeC6H4)Cl2,2c 627 kg-
PE/mol-V·h (ethylene 3 atm, in toluene, MAO cocatalyst, 50 °C,
30 min, Mw = 1.49 × 104, Mw/Mn = 3.0) by [Et(C5Me4)(NiPr)]
VCl2,2d 2243 kg-PE/mol-V·h (ethylene 6.8 atm, in toluene,
13 Polymerization procedure: Into a round bottom flask (10 mL
scale) containing norbornene (235 mg) dissolved in toluene (2.9
g), a toluene solution (1.0 g) containing 2 (13.2 mg, 25 µmol) was
added in one portion at room temperature. The mixture was
stirred for 11 h, and the solution was poured into methanol (200
mL). The resultant solid was collected by filtration and was
washed with methanol, and was then dried in vacuo. Yield; 87 mg
(37%). Molecular weight and molecular weight distribution were
measured by GPC (Shimadzu SCL-10A with RID-10A detector,
column: ShimPAC GPC-806, 804, and 802) in THF vs poly-
styrene standard. 1H NMR (CDCl3): δ 5.22 and 5.35 (br.m, 2H
olefinic), 2.80 and 2.37 (br.s, 2H), 1.85 and 1.08 (m, 2H), 1.81 and
1.36 (m, 4H). 13C NMR (CDCl3): δ 134.0, 133.9, 133.8, 133.7,
and 133.1, 133.0 and 132.8 (olefinic), 68.0, 50.8, 43.4, 43.2, 42.7,
42.1, 41.3, 38.6, 38.4, 33.1, 32.9, 32.3, 32.2, 25.6, 21.3.
MAO cocatalyst, 50 °C, 30 min, Mw = 17.42 × 104, Mw/Mn
=
50.79) by {2,6-bis[2,6-(iPr)2PhN=C(Me)]2(C5H3N)}VCl3
·1.3(CH2Cl2).2e
4
5
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14 Example concerning synthesis of high molecular weight ROMP
polymers, Y. Nakayama, H. Saito, N. Ueyama, and A. Nakamura,
Organometallics, 18, 3149 (1999).
15 Previous report concerning synthesis of vanadium–alkylidene
complex, see ref 8b.