Synthesis of half-titanocenes containing 1,3-imidazolidin-2-iminato ligands of type, Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N]: highly active catalyst precursors in ethylene (co)polymerisation

Abstract

A series of (pentamethylcyclopentadienyl)titanium(IV) dichloride complexes containing 1,3-imidazolidin-2-iminato ligands of type, Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu (1a), cyclohexyl (Cy, 1b), C₆H₅ (1c), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)] have been prepared and structures of 1b–e have been determined by X-ray crystallography. These complexes, especially 1d,e showed notable catalytic activities not only for ethylene polymerisation, but also for ethylene/1-hexene copolymerisation (activity 482 000–1 750 000 kg-polymer per mol-Ti per h) in the presence of MAO.

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Introduction

Polyolefins such as polyethylene [high density polyethylene (HDPE), linear low density polyethylene (LLDPE) etc.], isotactic polypropylene, are important commercial synthetic polymers, and metal catalysed olefin coordination polymerisation is known to be a core technology in industry. Recently, design of efficient molecular catalysts for precise olefin polymerisation attracts considerable attention (in terms of synthesis of new polymers) in the field of organometallic chemistry, catalysis, and of polymer chemistry.^1–4 It has been known since the early 1990's that linked half-titanocenes (called constrained geometry type, CGC, Chart 1), exemplified as [Me₂Si(C₅Me₄)(N^tBu)]TiCl₂, exhibit both high catalytic activity and comonomer incorporation in ethylene/α-olefin copolymerisation in the presence of a cocatalyst such as methylaluminoxane (MAO) or borate.³ In contrast, ordinary nonbridged (unlinked) half-titanocenes of type, Cp′TiX₃ (Cp′ = cyclopentadienyl group; X = F, Cl, OMe, alkyl etc., Chart 1), are known to be efficient catalyst precursors for synthesis of syndiotactic polystyrene (SPS);⁵ these complexes, however, showed low activities in ethylene polymerisation.

Chart 1 Selected examples for half-titanocenes as catalyst precursors for olefin polymerisation.^3–12

Recently, modified half-titanocenes (half-sandwich titanium complexes) containing anionic donor ligands of type, Cp′TiX₂(Y) (Cp′ = cyclopentadienyl group; X = halogen, alkyl; Y = aryloxo, ketimide, phosphinimide etc., Chart 1), are also recognised as the promising candidates,^4,6–12 especially in terms of syntheses of new polymers by ethylene copolymerisations⁴ with α-olefin,⁶ 2,2-disubstituted-1-olefins,¹⁰ norbornene¹¹ as well as with the other cyclic olefins,¹² as demonstrated by the aryloxo and the ketimide analogues.

Half-titanocenes containing imidazolidin-2-iminato ligands, first reported by Kretschmer and Hessen as CpTi(CH₂Ph)₂[1,3-(2,6-Me₂C₆H₃)₂(CH₂N)₂C=N],^8a have also been introduced as promising catalyst precursors for olefin polymerisation. This is because that the complex exhibited high catalytic activity for ethylene polymerisation in the presence of both B(C₆F₅)₃ and partially hydrolysed AlⁱBu₃ cocatalysts,^8a and that the activity was higher than those by the known ketimide analogue, CpTi(CH₂Ph)₂(N=C^tBu₂), and the phosphinimide analogue, CpTi(CH₂Ph)₂(N=P^tBu₂).^8a It has also been known that the imidazolin-2-iminato analogue, CpTiCl₂[1,3-^tBu₂(CHN)₂=N] (Chart 1), also exhibit high catalytic activities for ethylene polymerisation in the presence of MAO,⁹ affording ultrahigh molecular weight polymers.^9c Moreover, the complex shows notable catalytic activities for copolymerisation of ethylene with α-olefins^9c and was effective in ethylene/norbornene (NBE) copolymerisation for synthesis of high molecular weight poly(ethylene-co-NBE)s with high NBE contents.^9d

In these (imidazolidin-, imidazolin-2-iminato) ligand systems, a stabilisation by the zwitterionic resonance structures can be considered, affording strong basic nitrogen donor ligands with a high π-electron release capability, especially towards early transition metals with high oxidation state.^8,9 As demonstrated by the phenoxy- and/or ketimide-modified half-titanocenes,^4b–e efficient catalyst precursors for the desired (co)polymerisations would be tuned by the ligand modifications. We thus explored effect of the ligand substituents and reported that the Cp-^tBu analogue showed the highest catalytic activities among CpTiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu, cyclohexyl (Cy), C₆H₅, 2,6-Me₂C₆H₃] in ethylene polymerisation upon presence of MAO cocatalyst; the complex also exhibited superior catalyst performance (moderate comonomer incorporation with high activity) in ethylene/1-hexene copolymerisation.^8b Moreover, the activity by (^tBuC₅H₄)TiCl₂[1,3-^tBu₂(CH₂N)₂C=N] was similar to that by the Cp analogue in ethylene polymerisation, but showed low activity in ethylene/1-hexene copolymerisation (affording polymer with rather broad molecular weight distributions).^8c More recently, we realised that Cp*TiCl₂[1,3-(2,6-R′₂C₆H₃)₂–(CH₂N)₂C=N] (R′ = Me, ⁱPr) exhibit notable catalytic activities (in ethylene polymerisation) that are higher than those shown not only by the above catalysts, but also by the other known catalysts such as Cp*TiCl₂(O-2,6-ⁱPr₂C₆H₃),^6a,b CpTiCl₂(N=C^tBu₂),^7e CpTiCl₂[1,3-^tBu₂(CHN)₂=N].^9a,c We thus herein report synthesis of a series of the Cp* analogues, Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N], and explored results in ethylene (co)polymerisation in the presence of MAO (Scheme 1), especially their promising catalyst performances in ethylene/1-hexene copolymerisation.¹³

Scheme 1 Ethylene (co)polymerisation by Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] (1a–e)–MAO catalysts.

Results and discussion

Synthesis of half-titanocenes containing 1,3-imidazolidin-2-iminato ligands

A series of Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [Cp* = C₅Me₅; R = ^tBu (1a), Cy (1b), C₆H₅ (1c), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)], could be prepared from Cp*TiCl₃ by treating with Li[1,3-R₂(CH₂N)₂C=N], which was prepared in situ by treating 1,3-R₂(CH₂N)₂C=NH with ⁿBuLi in toluene (Scheme 2). This is the analogous method reported previously for syntheses of the Cp and ^tBuC₅H₄ analogues,^8b,c except using the lithium salts without isolation (prepared in situ). Use of toluene at 25 °C seems to be suited conditions for preparation of 1a, because Cp*TiCl₃ was recovered when Cp*TiCl₃ was treated with [1,3-^tBu₂(CH₂N)₂C=N]Li in toluene upon heating (50 or 70 °C).^8c The resultant complexes (1a–e) were identified by NMR spectra and elemental analysis, and structures of 1b–e were determined by X-ray crystallography (described below).¹⁴

Scheme 2 Synthesis of Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] (1a–e).

Yellow microcrystals of 1b–e that are suitable for X-ray crystallographic analyses were grown from the chilled CH₂Cl₂ solution (−30 °C) layered by n-hexane, and their structures are shown in Fig. 1. The selected bond distances and angles are summarised in Table 1.¹⁴

Fig. 1 Ortep drawings for Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = cyclohexyl (Cy, 1b, top left), C₆H₅ (1c, top right), 2,6-Me₂C₆H₃ (1d, bottom left), 2,6-ⁱPr₂C₆H₃ (1e, bottom right)]. Thermal ellipsoids are drawn at 50% probability level, and H atoms were omitted for clarity.¹⁴

Table 1 Selected bond distances (Å), angles (°) for Cp′TiCl₂[1,3-R₂(CH₂N)₂C=N] [Cp′ = Cp* (1), Cp (2), ^tBuC₅H₄ (3); R = ^tBu (1a), Cy (cyclohexyl, 1b), C₆H₅ (1c), 2,6-Me₂C₆H₃ (1–3d), 2,6-ⁱPr₂C₆H₃ (1e)]^a

Cp′	Cp*				Cp	^tBuC5H4
R	Cy (1b)	C6H5 (1c)	2,6-Me2C6H3 (1d)	2,6-^iPr2C6H3 (1e)	2,6-Me2C6H3 (2d)	2,6-Me2C6H3 (3d)
a Detailed data are shown in the ESI.^14
Bond distances (Å)
Ti(1)–Cl(1), Ti(1)–Cl(2)	2.3138(3), 2.3079(3)	2.3204(5), 2.3002(6)	2.2955(7), 2.3026(9)	2.3119(4), 2.2958(7)	2.3088(7), 2.3106(7)	2.2950(4), 2.3058(4)
Ti(1)–N(1)	1.7784(12)	1.8124(16)	1.7898(18)	1.8007(13)	1.7860(15)	1.7792(11)
N(1)–C(11)	1.3091(18)	1.296(3)	1.303(3)	1.3038(19)	N(1)–C(6) 1.308(3)	N(1)–C(10) 1.3053(15)
Ti(1)–C(2), Ti(1)–C(5)	2.3516(14), 2.4063(15)	2.3484(18), 2.3946(18)	2.352(3), 2.396(3)	2.3365(17), 2.401(2)	Ti(1)–C(1), Ti(1)–C(3) 2.406(2), 2.354(2)	Ti(1)–C(1), Ti(1)–C(3) 2.4711(11), 2.3213(17)
N(2)–C(11), N(3)–C(11)	1.3589(16), 1.3457(18)	1.360(3), 1.387(2)	1.359(3), 1.364(3)	1.3667(18), 1.3650(16)	N(2)–C(6), N(3)–C(6) 1.362(3), 1.353(3)	N(2)–C(10), N(3)–C(10) 1.3540(15), 1.3503(15)
N(2)–C(12), N(3)–C(13)	1.465(2), 1.4628(19)	1.468(3), 1.467(3)	1.465(3), 1.464(3)	1.4648(19), 1.471(2)	N(2)–C(7), N(3)–C(8) 1.468(3), 1.465(3)	N(2)–C(11), N(3)–C(12) 1.4678(18), 1.4653(17)
C(12)–C(13)	1.5368(18)	1.522(3)	1.526(4)	1.5296(19)	C(7)–C(8) 1.531(4)	1.534(2)
Bond angles (°)
Cl(1)–Ti(1)–Cl(2)	102.881(14)	100.921(19)	99.36(3)	100.257(19)	100.27(3)	101.971(17)
Ti(1)–N(1)–C(11)	170.98(10)	160.73(14)	177.15(16)	174.25(9)	Ti(1)–N(1)–C(6) 163.23(14)	Ti(1)–N(1)–C(10) 167.91(9)
Cl(1)–Ti(1)–N(1), Cl(2)–Ti(1)–N(1)	101.80(4), 104.31(3)	104.29(5), 104.60(5)	105.04(6), 104.71(6)	102.89(4), 104.11(6)	101.84(7), 106.80(6)	103.15(3), 102.21(3)

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The crystallographic analysis for complexes (1b–e) indicates that the complexes (1b–e) fold a distorted tetrahedral geometry around Ti, and the Ti–N bond distances [1.7784(12)–1.8124(16) Å] are relatively shorter than those in the Cp analogues [1.7650(16)–1.7918(17) Å]^8b and the ^tBuC₅H₄ analogues [1.7692(12)–1.8048(13) Å].^8c The distances are apparently shorter than those in (1,3-Me₂C₅H₃)TiCl₂[N(2,6-Me₂C₆H₃)-(SiMe₃)] [1.898(2) Å]^15a and Cp*TiCl₂[N(Me)(Cy)] [1.870(3) Å],^15b but are close to or longer than those in half-sandwich titanium complexes containing imidazolin-2-iminato ligands, CpTiCl₂[1,3-R₂(CHN)₂C=N], [1.765(3), 1.768(2), and 1.778(2) Å in R = ^tBu, ⁱPr, 2,6-ⁱPr₂C₆H₃, respectively].^9b These results suggest both the titanium and nitrogen in 1b–e form σ-bond especially in addition to strong π-donation from the nitrogen to Ti; the π-donation would be strong compared to the complexes exemplified above^6a,b probably due to a high π-electron release capability stabilised by the zwitterionic resonance structures (as described above).^8,9

The Ti–Cl bond distances and the Cl(1)–Ti(1)–Cl(2) bond angles in 1b–e [2.2955(7)–2.3204(5) Å; 99.36(3)–102.881(14)°] are relatively close to those in the Cp analogues [2.2902(7)–2.3124(5) Å; 100.27(3)–105.14(2)°, respectively]^8b as well as the ^tBuC₅H₄ analogues [2.2917(5)–2.3142(4) Å; 97.730(15)–103.585(17)°, respectively],^8c and are close to those in the imidazolin-2-iminato analogues, CpTiCl₂[1,3-R₂(CHN)₂C=N] [2.2977(8)–2.3253(6) Å, 99.22(2)–100.49(3)°; R = ^tBu, ⁱPr, 2,6-ⁱPr₂C₆H₃, respectively].^8b

It might be interesting to note that the Ti(1)–N(1)–C(11) bond angles in 1d,e [177.15(16), 174.25(9)°, respectively] are larger than those in the Cp analogue [163.23(14)°]^8b and the ^tBuC₅H₄ analogue [167.91(9)°] (Table 1).^8c The angles are slightly larger than those in CpTiCl₂[1,3-^tBu₂(CH₂N)₂C=N] [172.08(17)°],^8b CpTiCl₂[1,3-^tBu₂(CHN)₂C=N] [170.7(2)°],^8c (^tBuC₅H₄)TiCl₂[1,3-^tBu₂(CHN)₂C=N] [172.6(2)°],^9b but is close to that in (^tBuC₅H₄)TiCl₂[1,3-^tBu₂(CH₂N)₂C=N] [175.69(10)°],^9b which showed high activity for ethylene polymerisation. Almost linear Ti–N–C bond angle in 1d,e is indicative of efficient ligand-to-metal π-donation, as previously observed by Cp*TiCl₂(O-2,6-ⁱPr₂C₆H₃) [Ti–O–C 173.0(3)°], which exhibited notable activity in ethylene (co)polymerisation in the presence of cocatalysts.^6a,b

Ethylene polymerisation and ethylene copolymerisation by Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu, Cy, C₆H₅, 2,6-Me₂C₆H₃, 2,6-ⁱPr₂C₆H₃]–MAO catalysts

Ethylene polymerisation by Cp′TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu (1a), Cy (1b), C₆H₅ (1c), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)]–MAO catalysts. Ethylene polymerisations by Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu (1a), Cy (1b), C₆H₅ (1c), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)] were conducted in toluene in the presence of d-MAO (prepared as the white solid by removal of toluene and AlMe₃ from commercially available sample, Tosoh Finechem, TMAO) at 25 °C, and the results are summarised in Table 2. Plots of the catalytic activity (kg-PE per mol-Ti per h) vs. MAO (mmol) in the polymerisation are also shown in Fig. 2.

Table 2 Ethylene polymerisation by Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu (1a), Cy (1b), C₆H₅ (1c), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)]–MAO catalysts^a

Run	Complex (μmol)	R	MAO/mmol	Yield/mg	Activity/kg-PE per mol-Ti per h
a Conditions: toluene + minimum quantity of CH2Cl2 total 30 mL, ethylene 6 atm, d-MAO (prepared by removing toluene and AlMe3 from ordinary MAO), 25 °C, 10 min.
1	1a (0.02)	^tBu	0.20	29	8580
2	1a (0.02)	^tBu	1.0	32	9510
3	1a (0.02)	^tBu	2.0	30	9030
4	1a (0.02)	^tBu	3.0	27	8130
5	1b (0.2)	Cy	0.50	10	300
6	1b (0.2)	Cy	1.0	30	900
7	1b (0.2)	Cy	2.0	85	2550
8	1b (0.2)	Cy	3.0	84	2520
9	1b (0.2)	Cy	4.0	68	2040
10	1b (0.2)	Cy	5.0	70	2100
11	1c (0.05)	C6H5	1.0	20	2400
12	1c (0.05)	C6H5	2.0	26	3120
13	1c (0.05)	C6H5	3.0	37	4440
14	1c (0.05)	C6H5	4.0	54	6480
15	1c (0.05)	C6H5	5.0	52	6240
16	1c (0.05)	C6H5	6.0	56	6720
17	1c (0.05)	C6H5	1.0	20	2400
18	1d (0.02)	2,6-Me2C6H3	0.10	214	64 100
19	1d (0.02)	2,6-Me2C6H3	0.20	371	111 000
20	1d (0.02)	2,6-Me2C6H3	1.0	238	71 400
21	1d (0.02)	2,6-Me2C6H3	2.0	220	65 900
22	1d (0.02)	2,6-Me2C6H3	3.0	231	69 300
23	1d (0.02)	2,6-Me2C6H3	4.0	249	74 700
24	1e (0.02)	2,6-^iPr2C6H3	0.20	140	41 900
25	1e (0.02)	2,6-^iPr2C6H3	1.0	328	98 500
26	1e (0.02)	2,6-^iPr2C6H3	2.0	399	120 000
27	1e (0.02)	2,6-^iPr2C6H3	3.0	430	129 000
28	1e (0.02)	2,6-^iPr2C6H3	4.0	417	125 000

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Fig. 2 Plots of catalytic activity (kg-PE per mol-Ti per h) vs. MAO (mmol) in ethylene polymerisation using Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu (1a), Cy (1b), C₆H₅ (1c), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)]. Top: complex 1a–e; bottom: complexes 1a–c (expanded). Detailed data are shown in Table 2.

It turned out, as shown in Table 2 and Fig. 2, that the activity was affected by Al/Ti molar ratio (amount of d-MAO) and the optimised ratio was dependent upon the catalyst precursor (1a–e) employed. The catalytic activity by Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] (1a–e) under the optimised conditions increased in the order: 1b (R = Cy; 2550 kg-PE per mol-Ti per h) < 1c (R = C₆H₅; 6720) < 1a (R = ^tBu; 9510) ≪ 1d (R = 2,6-Me₂C₆H₃; 111 000), 1e (R = 2,6-ⁱPr₂C₆H₃; 129 000). As summarised in Table 3, the order by the Cp* analogues is apparently different from those by the Cp analogues, CpTiCl₂[1,3-R₂(CH₂N)₂C=N] [2b (R = Cy; 2070 kg-PE per mol-Ti per h) < 2d (R = 2,6-Me₂C₆H₃; 2220), 2c (R = C₆H₅; 2580) ≪ 2a (R = ^tBu; 12 700)],^8b and the ^tBuC₅H₄ analogues, (^tBuC₅H₄)TiCl₂[1,3-R₂(CH₂N)₂C=N] [3b (220 kg-PE per mol-Ti per h) < 3d (960), 3c (2120) ≪ 3a (15 000)];^8c the ^tBu analogues (2a, 3a) showed the exceptionally highest activity. We previously assumed that reason for the high activity would be due to rather large Ti–N–C bond angle in the imidazolidin-2-iminato ligand [172.08(17), 175.69(10)° for 2a, 3a, respectively],^8b,c which would affect a strong ligand-to-metal π-donation for stabilisation of the catalytically-active species.^6a As described above, complexes 1d,e also possess large bond angles [177.15(16), 174.25(9)°, respectively], therefore, we assume that reason for the high activity by 1d,e would be due to a rather strong electron donating nature due to their unique bond angles.

Table 3 Selected results in ethylene polymerisation by Cp′TiCl₂[1,3-R₂(CH₂N)₂C=N] [Cp′ = Cp* (1), Cp (2), ^tBuC₅H₄ (3); R = ^tBu (a), Cy (b), C₆H₅ (c), 2,6-Me₂C₆H₃ (d), 2,6-ⁱPr₂C₆H₃ (e)]–MAO catalysts.^a Effect of ligand(s) in ethylene polymerisation^a

Run	Complex (μmol)			MAO/mmol	Activity^b
	Cp′	R
a Conditions: toluene + minimum quantity of CH2Cl2 total 30 mL, ethylene 6 atm, d-MAO (prepared by removing toluene and AlMe3 from ordinary MAO), 25 °C, 10 min.b Activity in kg-PE per mol-Ti per h.c Cited from ref. 8b.d Cited from ref. 8c.e Cited from ref. 16.f Cited from ref. 7e.g Cited from ref. 9c.
2	Cp*	^tBu	1a (0.02)	1.0	9510
7	Cp*	Cy	1b (0.2)	2.0	2550
8	Cp*	Cy	1b (0.2)	3.0	2520
14	Cp*	C6H5	1c (0.05)	4.0	6480
16	Cp*	C6H5	1c (0.05)	6.0	6720
19	Cp*	2,6-Me2C6H3	1d (0.02)	0.20	111 000
27	Cp*	2,6-^iPr2C6H3	1e (0.02)	3.0	129 000
29^c	Cp	^tBu	2a (0.05)	0.10	12 700
30^c	Cp	Cy	2b (0.2)	3.0	2070
31^c	Cp	C6H5	2c (0.1)	3.0	2580
32^c	Cp	2,6-Me2C6H3	2d (0.1)	3.0	2220
33^d	^tBuC5H4	^tBu	3a (0.02)	1.0	15 000
34^d	^tBuC5H4	Cy	3b (0.5)	2.0	220
35^d	^tBuC5H4	C6H5	3c (0.3)	0.05	2120
36^d	^tBuC5H4	2,6-Me2C6H3	3d (0.4)	1.0	960
37^e	Cp*TiCl2(O-2,6-^iPr2C6H3)		(0.01)	3.0	43 200
38^f	CpTiCl2(N=C^tBu2)		(0.2)	3.0	19 100
39^g	CpTiCl2[1,3-^tBu2(CHN)2C=N]		(0.01)	0.50	51 000
40^g	(^tBuC5H4)TiCl2[1,3-^tBu2(CHN)2C=N]		(0.005)	0.50	66 000

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Note that the activities by 1d,e (run 19, 27: activity = 111 000, 129 000 kg-PE per mol-Ti per h, respectively) are not only higher than those by the ^tBu analogues, Cp′TiCl₂[1,3-^tBu₂(CH₂N)₂C=N] [Cp′ = Cp* (1a, run 2, activity = 9510), Cp (2a, run 29, 12 700), ^tBuC₅H₄ (3a, run 33, 15 000)], but also higher than those by reported Cp*TiCl₂(O-2,6-ⁱPr₂C₆H₃) (run 37, activity = 43 200 kg-PE per mol-Ti per h),¹⁶ CpTiCl₂(N=C^tBu₂) (run 38, 19 100),^7e Cp′TiCl₂[1,3-^tBu₂(CHN)₂C=N] [Cp′ = Cp (run 39), ^tBuC₅H₄ (run 40), activity = 51 000, 66 000 kg-PE per mol-Ti per h, respectively],^9c which are known to exhibit high catalytic activities in ethylene polymerisation with this type (Table 3). It is thus clear that 1d,e would be promising catalysts for ethylene polymerisation.

Copolymerisation of ethylene with 1-hexene, styrene, or with norbornene by Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu (1a), Cy (1b), C₆H₅ (1a), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)]–MAO catalysts. Table 4 summarises results in copolymerisation of ethylene with 1-hexene by Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu (1a), Cy (1b), C₆H₅ (1c), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)] in the presence of MAO cocatalyst. The data by the Cp analogues (2a–d), the ^tBuC₅H₄ analogues (3a–d) conducted under the same conditions are also placed for comparison. As reported previously,^{6c,e,7e,8,9c,d} these copolymerisations were terminated for 10 min (at rather initial stage) to control low comonomer conversion (less than 10 mol%).

Table 4 Ethylene/1-hexene copolymerisation by Cp′TiCl₂[1,3-R₂(CH₂N)₂C=N] [Cp′ = Cp* (1), Cp (2), ^tBuC₅H₄ (3); R = ^tBu (a), Cy (b), C₆H₅ (c), 2,6-Me₂C₆H₃ (d), 2,6-ⁱPr₂C₆H₃ (e)]–MAO catalysts^a

Run	Complex (μmol)	MAO/mmol	1-Hexene /mL	Yield/ mg	Activity^b	Mn^c × 10^−4	Mw/Mn^c	Cont.^d/mol%
a Conditions: toluene + minimum quantity of CH2Cl2 + 1-hexene total 30 mL, ethylene 6 atm, d-MAO (prepared by removing toluene and AlMe3 from ordinary MAO), 25 °C, 10 min.b Activity = kg-polymer per mol-Ti per h.c GPC data in o-dichlorobenzene vs. polystyrene standards.d 1-Hexene content (mol%) estimated by ^13C NMR spectra.e Insoluble for GPC measurement.f Cited from ref. 8b.g Cited from ref. 8c.h Cited from ref. 7e.
41	1a (0.2)	4.0	3.0	167	5000	Insoluble^e
42	1b (4.0)	2.0	5.0	30	50	14.7	2.40
43	1c (0.4)	4.0	5.0	44	660	43.9	2.39	1.8
44	1d (0.0005)	0.10	3.0	146	1 750 000	113	2.09	16.4
45	1d (0.001)	0.10	5.0	138	82 8000	121	2.30	26.5
46	1e (0.0005)	3.0	3.0	69	822 000	78.7	1.76
47	1e (0.002)	3.0	5.0	161	482 000	61.4	2.03
48^f	2a (0.1)	0.10	5.0	77	4620	94.7	1.72	28.6
49^f	2b (4.0)	3.0	5.0	21	30	1.73	12.6
50^f	2c (3.0)	3.0	5.0	74	150	0.12	54.0
51^f	2d (2.0)	3.0	5.0	100	300	6.62	4.39
52^g	3a (0.5)	1.0	5.0	38	460	8.15	3.60^h
53^g	3b (6.0)	2.0	5.0	32	30	4.17	2.86
54^g	3c (10)	0.05	5.0	Trace	Trace
55^g	3d (0.4)	1.0	5.0	80	1200	71.6	2.19	14.8
56	CpTiCl2(N=C^tBu2)^h (0.01)	3.0	5.0	190	114 000	70.4	2.40	26.9

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Note that 1d,e exhibited the remarkable catalytic activities (runs 44–47, activity 482 000–1 750 000 kg-polymer per mol-Ti per h). The activity by 1a–e under the optimised conditions increased in the order: 1b (R = Cy, run 42) < 1c (R = C₆H₅, run 43) < 1a (R = ^tBu, run 41) ≪ 1d (R = 2,6-Me₂C₆H₃, runs 44–45), 1e (R = 2,6-ⁱPr₂C₆H₃, runs 46–47). The observed activities by 1d,e are much higher than those not only by 2a–d (4620 by 2a, run 48)^8b and 3a–d (1200 by 3d, run 55),^8c but also by CpTiCl₂(N=C^tBu₂) (114 000 kg-polymer per mol-Ti per h)^7e under the same conditions. Moreover, 1d showed higher activity than 1e. The resultant polymers prepared by 1d,e possessed high molecular weight with unimodal molecular weight distributions (M_n = 6.14–12.1 × 10⁵, M_w/M_n = 1.76–2.30). These results (unimodal molecular weight distributions in the resultant polymers by 1d,e) thus suggest that these copolymerisation proceed with uniform catalytically active species. The results also clearly suggest that fine-tuning of both cyclopentadienyl ligand (Cp′) and substituents on the imidazolidin-2-iminato ligand plays an essential role for exhibiting the remarkable activity.

Table 5 summarises ethylene/1-hexene copolymerisation results by 1d,e–MAO catalysts under various conditions. It turned out that the activity on the basis of polymer yield decreased upon increasing 1-hexene charged (1-hexene concentration in the reaction mixture) with increase in the comonomer contents (runs 44–45, 46–47, 60–61). It seems that the M_n values in the resultant copolymers prepared by 1d were not affected by the 1-hexene content (runs 44, 45, 57), possessing ultrahigh molecular weights; this would be one of the unique characteristics by using 1d as the catalyst precursor. In contrast, the M_n value in the copolymer prepared by the 2,6-ⁱPr₂C₆H₃ analogue (1e) seems decreasing upon increasing the 1-hexene contents (runs 46, 47, 60, 61). It also turned out that the activity by 1e increased upon addition of AlMe₃, without decrease in the M_n value in the resultant copolymer (run 59); the results may thus suggest that β-hydrogen elimination (after 1-hexene insertion) as the major chain-transfer in this catalysis.

Table 5 Copolymerisation of ethylene with 1-hexene by Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)]–MAO catalysts^a

Run	Complex (μmol)	Ethylene/atm	1-Hexene/mL	Yield/mg	Activity^b	Mn^c × 10^−5	Mw/Mn^c	Cont.^d/mol%
a Conditions: toluene + 1-hexene + minimum quantity of CH2Cl2 total 30 mL, ethylene, d-MAO (prepared by removing toluene and AlMe3 from ordinary MAO) 0.1 mmol (1d) or 3.0 mmol (1e) 25 °C, 10 min.b Activity = kg-polymer per mol-Ti per h.c GPC data in o-dichlorobenzene vs. polyethylene standards.d 1-Hexene content (mol%) estimated by ^13C NMR spectra.e 1-Dodecene used in place of 1-hexene.f Copolymerisation in the presence of AlMe3 (AlMe3/Ti = 500).
44	1d (0.0005)	6	3.0	146	1 750 000	11.3	2.09	16.4
45	1d (0.001)	6	5.0	138	828 000	12.1	2.30	26.5
57	1d (0.003)	4	5.0	58	116 000	13.1	2.13	44.2
58	1d (0.004)	6	5.0^e	27	40 500	6.81	3.51	3.7
46	1e (0.0005)	6	3.0	69	822 000	7.87	1.76
59	1e (0.001)^f	6	3.0	171	1020 000	6.40	1.75
47	1e (0.002)	6	5.0	161	482 000	6.14	2.03
60	1e (0.005)	4	5.0	98	118 000	4.70	2.09	33.3
61	1e (0.008)	4	10.0	128	96 200	4.16	2.10	48.9

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It also turned out that 1-hexene contents (estimated by ¹³C NMR spectra shown below) in the resultant poly(ethylene-co-1-hexene)s prepared by 1d–MAO catalyst were higher than those by 1e–MAO catalyst. The C₆H₅ analogue (1c), however, showed inefficient 1-hexene incorporation (run 43): these results thus suggest that the substituent on the imidazolidin-2-iminato ligand strongly affect the 1-hexene incorporation. It is clear that 1d is the most suited catalyst precursor among 1a–e in terms of both the activity and 1-hexene incorporation.

Fig. 3 shows typical ¹³C NMR spectra (in 1,2,4-trichloro-benzene/C₆D₆ at 110 °C) of the resultant poly(ethylene-co-1-hexene)s prepared by 1d,e–MAO catalysts, and results in the triad sequence distributions¹⁷ as well as the r_E, r_H and the r_E·r_H values estimated by the spectra (and the initial monomer conc.) are also summarised in Table 6.^17,18 In the copolymers prepared by 1d–MAO catalyst (Fig. 3a and b), resonances ascribed to alternating 1-hexene incorporation [ca. 38 ppm (T_δδ, CH_EHE), 35.5 ppm (S_αγ), 24.4 ppm (S_ββ) etc.] in addition to those ascribed to the isolated 1-hexene incorporation were clearly observed, but resonances ascribed to HHH repeat units (40–42 ppm) were negligible (or very small). In contrast, resonances ascribed to 1-hexene repeated incorporation [40–42 ppm (S_αα), 36.1 ppm (T_βδ)] were observed in the poly(ethylene-co-1-hexene)s prepared by 1e–MAO catalyst (Fig. 3c), although 1e showed less efficient 1-hexene incorporation in this catalysis (Table 6). These would affect a ratio of EHE : EHH + HHE by 1d,e, summarised in Table 6.

Fig. 3 ¹³C NMR spectrum (in 1,2,4-trichlorobenzene/C₆D₆ at 110 °C) of the resultant poly(ethylene-co-1-hexene) prepared by (a and b) 1d (runs 45, 57, respectively), (c) 1e (run 60) in the presence of MAO cocatalyst.

Table 6 Monomer sequence distributions of poly(ethylene-co-1-hexene)s prepared by copolymerisation of ethylene (E) with 1-hexene (H) by Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = C₆H₅ (1c), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)]–MAO catalysts^a

Run	Complex	Cont.^b/mol%	Triad sequence distribution^c (%)						Dyad^d			rE·rH^e	rE^f	rH^f
			EEE	EEH + HEE	HEH	EHE	HHE + EHH	HHH	EE	EH + HE	HH
a For detailed polymerisation conditions, see Tables 4 and 5.b 1-Hexene content (mol%) estimated by ^13C NMR spectra.c Determined by ^13C NMR spectra.d [EE] = [EEE] + 1/2[EEH + HEE], [EH] = [HEH] + [EHE] + 1/2{[EEH + HEE] + [HHE + EHH]}, [HH] = [HHH] + 1/2[HHE + EHH].e rE × rH = 4[EE][HH]/[EH + HE]2.f rE = [H]0/[E]0 × 2[EE]/[EH + HE], rH = [E]0/[H]0 × 2[HH]/[EH + HE], [E]0 and [H]0 are the initial monomer concentrations.g Data by CpTiCl2[1,3-^tBu2(CH2N)2C=N] (2a) cited from ref. 8b.h Data by CpTiCl2(N=C^tBu2) (Cp-Ket) cited from ref. 7e.
43	1c	1.8	94.6	3.6	—	1.7	0.1	—	96.4	3.6	—	0.92	98.5	0.009
44	1d	16.4	57.9	22.7	3.0	12.6	3.8	—	69.3	28.9	1.8	0.62	5.26	0.12
45	1d	26.5	43.6	26.0	3.8	18.0	8.6	—	56.6	39.1	4.3	0.63	5.29	0.12
57	1d	44.2	26.0	22.6	7.2	21.3	22.9	—	37.3	51.2	11.5	0.65	3.98	0.16
60	1e	33.3	43.1	21.0	2.7	9.9	23.4	—	59.9	37.9	2.2	0.36	7.89	0.045
48	2a^g	28.6	41.4	24.4	5.6	14.8	13.8	—	53.6	39.5	6.9	0.94	4.95	0.19
56	Cp-Ket^h	26.9	34.5	30.7	7.9	20.5	5.2	1.2	49.9	46.4	3.8	0.35	4.5	0.08

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As summarised in Table 6, the r_E·r_H values by 1d were 0.65, suggesting that the copolymerisation by 1d–MAO catalyst system proceeded in a random manner (1-hexene incorporations were random in this catalysis). The r_E values (in runs 44–45) by 1d are 5.26–5.29, and the value is close to that by CpTiCl₂[1,3-^tBu₂(CH₂N)₂C=N] (2a, r_E = 4.95, run 48), but is lower than those in the Cp-imidazolin-2-iminato analogues (9.56–11.8).^9c The value is also somewhat similar to those by ansa-metallocenes,¹⁹ but is slightly larger than that in CpTiCl₂(N=C^tBu₂) (4.5, run 56).^7e Note that the r_E values are strongly affected by the substituent on the imidazolidin-2-iminato ligand (by 1c–e, shown in Table 6). These results thus suggest that a precise modification of the anionic donor ligand plays an important role for the copolymerisation to proceed with uniform catalytically active species as well as with moderate 1-hexene incorporation. On the basis of these results (Tables 4–6), 1d exhibits superior catalyst performance in ethylene/1-hexene copolymerisation in terms of both activity and 1-hexene incorporation.

Table 7 summarises results in ethylene/styrene copolymerisation by 1d–MAO catalyst under the reported conditions for (^tBuC₅H₄)TiCl₂[1,3-(2,6-Me₂C₆H₃)₂(CH₂N)₂C=N] (3d)–MAO catalyst (run 65).^8c The resultant polymers were poly(ethylene-co-styrene)s as acetone insoluble and THF soluble fractions, that possess uniform composition confirmed by DSC thermograms.²⁰ Styrene contents in the copolymers by 1d were lower than that by 3d conducted under the same conditions, suggesting 1d showed less efficient catalyst precursor compared to 3d (runs 62–65).

Table 7 Copolymerisation of ethylene with styrene by Cp*TiCl₂[1,3-(2,6-Me₂C₆H₃)₂(CH₂N)₂C=N] (1d)–MAO catalyst^a

Run	Complex (μmol)	Styrene/mL	Yield^b/mg	Activity^c	Mn^d × 10^−5	Mw/Mn^d	Tm^e/°C	St. cont.^f/mol%
a Conditions: toluene + styrene + minimum quantity of CH2Cl2 total 30 mL, ethylene 4 atm, d-MAO (prepared by removing toluene and AlMe3 from ordinary MAO) 0.1 mmol 25 °C, 10 min.b Polymer yield based on acetone insoluble and THF soluble fractions.c Activity = kg-polymer per mol-Ti per h.d GPC data in o-dichlorobenzene vs. polyethylene standards.e Melting temperature by DSC thermogram.f Styrene content (mol%) estimated by ^1H NMR spectra.g Data by (^tBuC5H4)TiCl2[1,3-(2,6-Me2C6H3)2(CH2N)2C=N] (3d) cited from ref. 8c.
62	1d (0.2)	5.0	66	1980	4.26	3.14	119.1	0.9
63	1d (0.2)	10.0	30	900	3.26	2.60	115.1	2.8
64	1d (0.3)	15.0	38	760	2.51	2.45	112.3	4.4
65	3d (2.0)^g	5.0	34	100	7.21	1.52	99.7	6.8

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Since it has been known that CpTiCl₂(N=C^tBu₂) exhibits remarkable both catalytic activity and comonomer incorporations in ethylene copolymerisation with norbornene (NBE),^11b the copolymerisation of ethylene with NBE using 1a,d,e–MAO catalysts were thus conducted under the similar conditions and the results are summarised in Table 8. Although 1d showed the remarkable activities (runs 67–69), the NBE contents estimated by DSC thermograms are low. This is because both melting temperature (T_m) and glass transition temperature (T_g) were observed in the resultant polymer prepared by 1d–MAO catalyst under certain conditions (run 67), whereas the resultant polymer prepared by the related imidazolin-2-iminato analogue, CpTiCl₂[1,3-^tBu₂(CHN)₂–C=N], possess rather high T_g values (with rather high NBE content, 34.4 mol%, run 73);^9d CpTiCl₂(NC^tBu₂) showed superior catalyst performance (run 74).^11b Both 1a and 1e showed less NBE incorporations than 1d as well as the other two complexes shown in Table 8, although 1e showed higher activity than 1d.^9d,11b These results thus suggest that monomer reactivity (NBE incorporation) was affected by substituents on the imidazolidin-2-iminato ligands.

Table 8 Copolymerisation of ethylene with norbornene (NBE) by Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu (a), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)]–MAO catalysts^a

Run	Complex/μmol	NBE^b/M	Yield /mg	Activity^c	Mn^d × 10^−5	Mw/Mn^d	Tm^e (Tg^e)/°C
a Conditions: toluene + (minimum quantity of CH2Cl2) + NBE total 30 mL, d-MAO 1.0 mmol, 25 °C, ethylene 6 atm, 10 min.b Initial NBE conc. (mol L^−1).c Activity in kg of polymer per mol-Ti per h.d GPC data in o-dichlorobenzene vs. polystyrene standards.e By DSC thermogram.f Total volume 10 mL.g Polymerisation at 60 °C.h Cited from ref. 9d, NBE 34.4 mol%.i Cited from ref. 11b, ethylene 4 atm, NBE 40.7 mol%.
66	1a (0.2)	2.5	182	2190	20.0	2.94	130
67	1d (0.05)	2.5	80	9560	16.9	4.42	38, (−6)
68^f	1d (0.08)	5.0	144	10 800	2.92	1.25	(5)
69^f^,^g	1d (0.05)	5.0	113	13 600	2.49	1.33	(18)
70	1e (0.05)	2.5	162	19 500	37.6	2.91	90
71^f	1e (0.04)	5.0	155	18 600	6.12	2.12	75
72^f^,^g	1e (0.05)	5.0	149	17 900	4.28	2.29	72
73	CpTiCl2[1,3-^tBu2-(CHN)2C=N]^h (0.10)	2.0	107	6410	11.1	1.94	(116.2)
74	CpTiCl2(N=C^tBu2)^i (0.01)	1.0	134	40 200	7.19	2.90

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Conclusions

A series of Cp*TiCl₂[1,3-R₂(CH₂N)₂C=N] [R = ^tBu (1a), cyclohexyl (Cy, 1b), C₆H₅ (1c), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)] have been prepared, identified, and structures of 1b–e have been determined by X-ray crystallography; complexes 1d,e possess large Ti–N(1)–C(11) bond angles [177.15(16), 174.25(9)°, respectively]. Complexes 1d,e exhibited notable catalytic activities for ethylene polymerisation in the presence of MAO cocatalyst, and the activities (111 000, 129 000 kg-PE per mol-Ti per h, respectively) are not only much higher than those by the Cp analogues (2a–d) and the ^tBuC₅H₄ analogues (3a–d), but also higher than those by the known active catalysts such as Cp*TiCl₂(O-2,6-ⁱPr₂C₆H₃),¹⁶ CpTiCl₂(N=C^tBu₂),^7e Cp′TiCl₂[1,3-^tBu₂(CHN)₂C=N] (Cp′ = Cp, ^tBuC₅H₄)^9c conducted under the similar conditions. Moreover, complexes 1d,e exhibited exceptionally remarkable catalytic activities for ethylene/1-hexene copolymerisation (482 000–1 750 000 kg-polymer per mol-Ti per h), and 1d especially afforded ultrahigh molecular weight poly(ethylene-co-1-hexene)s with uniform molecular weight distributions (M_n = 1.13–1.31 × 10⁶, M_w/M_n = 2.09–2.30). We highly believe the results through this study should be promising for better design of the catalyst for precise olefin polymerisation. We are on the way to demonstrate unique characteristics of using this catalyst in terms of synthesis of new polymers by ethylene copolymerisation, and hope to introduce them in the near future.

Experimental section

General procedures

All experiments were carried out under a nitrogen atmosphere in a vacuum atmospheres drybox unless otherwise specified. All chemicals used were of reagent grade and were purified by the standard purification procedures. Anhydrous grade toluene, n-hexane, dichloromethane, tetrahydrofuran, and diethyl ether (Kanto Chemical Co., Inc.) were transferred into bottles containing molecular sieves (mixture of 3 Å 1/16 and 4 Å 1/8, and 13× 1/16) under a nitrogen stream in the drybox and were used without further purification. 1,3-^tBu₂(CH₂N)₂C=NH,^8b 1,3-(cyclo-C₆H₁₃)₂(CH₂N)₂C=NH,^8b 1,3-(C₆H₅)₂(CH₂N)₂C=NH,^8a 1,3-(2,6-Me₂C₆H₃)₂(CH₂N)₂C=NH,^8b 1,3-(2,6-ⁱPr ₂C₆H₃)₂(CH₂N)₂C=NH²¹ were prepared according to the reported procedure. Polymerisation grade ethylene (purity > 99.9%, Sumitomo Seika Co. Ltd) was used as received. Toluene and AlMe₃ in the commercially available methylaluminoxane [TMAO, 9.5 wt% (Al) toluene solution, Tosoh Finechem Co.] were removed under reduced pressure (at ca. 50 °C for removing toluene, AlMe₃, and then heated at >100 °C for 1 h for completion) in the drybox to give white solids. Ethylene for polymerisation was of polymerisation grade (purity > 99.9%, Sumitomo Seika Co., Ltd) and was used as received. Elemental analyses were performed by using a PE2400II Series (Perkin-Elmer Co.).

All ¹H and ¹³C NMR spectra were recorded on a JEOL JNMLA400 spectrometer (399.65 MHz, ¹H; 100.40 MHz, ¹³C) or Bruker AV500 spectrometer (500.13 MHz, ¹H; 125.77 MHz, ¹³C) and all chemical shifts are given in ppm and are referred to SiMe₄. ¹³C NMR spectra for the resultant polymers were recorded with proton decoupling, and the pulse interval was 5.2 s, the acquisition time was 0.8 s, the pulse angle was 90°, and the number of transients accumulated was ca. 6000. The copolymer samples for analysis were prepared by dissolving the polymers in 1,1,2,2-tetrachloroethane-d₂ solution (for ¹H NMR spectra) or in 1,2,4-trichlorobenzene-benzene-d₆ (for ¹³C NMR spectra), and the spectra was measured at 80 °C or 110 °C (for ¹H, ¹³C NMR spectra, respectively).

Molecular weights and molecular weight distributions for the resultant polymers were measured by gel permeation chromatography (Tosoh HLC-8121GPC/HT) using a RI-8022 detector (for high temperature; Tosoh Co.) with a polystyrene gel column (TSK gel GMHHR-H HT × 2, 30 cm × 7.8 mm i.d., ranging from <10² to <2.8 × 10⁸ MW) at 140 °C using o-dichlorobenzene containing 0.05 wt/v% 2,6-di-tert-butyl-p-cresol as the solvent. The molecular weight was calculated by a standard procedure based on the calibration with standard polystyrene samples.

Synthesis of Cp*TiCl₂[1,3-^tBu₂(CH₂N)₂C=N] (1a). Into a toluene solution (5.0 mL) containing 1,3-^tBu₂(CH₂N)₂C=NH (130 mg, 0.66 mmol), ⁿBuLi (0.66 mmol, 1.6 M in n-hexane) was added at −30 °C. The reaction mixture was stirred for 3 h, and cooled into the freezer (−30 °C). The mixture was then added a toluene solution (1.0 mL) containing Cp*TiCl₃ (191 mg, 0.66 mmol), the reaction solution was stirred overnight at 25 °C. The resultant reaction mixture was added dichloromethane and was placed in vacuo to remove volatiles. The resultant solid was extracted with hot toluene. The chilled solution (stored in the freezer at −30 °C) afforded yellow microcrystals. Yield 104 mg (35%). ¹H NMR (CDCl₃): δ 1.39 (s, 18H, NCMe₃), 2.10 (s, 15H, C₅Me₅), 3.31 (s, 4H, NCH₂CH₂N). ¹³C NMR (CDCl₃): δ 13.3 (C₅Me₅), 29.3 (NCMe₃), 42.6 (NCH₂CH₂N), 56.1 (NCMe₃), 127.4 (C₅Me₅), 156.6 (N₂CN). Anal. calcd. for C₂₁H₃₇Cl₂N₃Ti: C, 56.01; H, 8.28; N, 9.33%. Found: C, 56.10; H, 7.93; N, 9.26%.

Synthesis of Cp*TiCl₂[1,3-Cy₂(CH₂N)₂C=N] (1b). Synthesis of 1b was conducted similarly as that for 1a, except that Cp*TiCl₃ (400 mg, 1.38 mmol), 1,3-Cy₂(CH₂N)₂C=NH (344 mg, 1.38 mmol) and 1 equiv. of ⁿBuLi (1.38 mmol, 1.6 M in n-hexane) were used. After the similar purification procedure, orange microcrystals were obtained from the chilled solution (−30 °C). Yield 451 mg (65%). ¹H NMR (CDCl₃): δ 1.38 (m, 20H, NCHC₅H₁₀), 2.11 (s, 15H, C₅Me₅), 3.31 (s, 4H, NCH₂CH₂N), 3.76 (brs, 2H, NCHC₅H₁₀). ¹³C NMR (CDCl₃): δ 12.9 (C₅Me₅), 25.6 (NCHC₂H₄C₃H₆), 30.7 (NCHC₂H₄C₃H₆), 39.9 (NCH₂CH₂N), 52.8 (NCHC₅H₁₀), 125.9 (C₅Me₅), 153.0 (N₂CN). Anal. calcd for C₂₅H₄₁Cl₂N₃Ti: C, 59.77; H, 8.23; N, 8.36%. Found: C, 59.67; H, 8.33; N, 8.31%.

Synthesis of Cp*TiCl₂[1,3-(C₆H₅)₂(CH₂N)₂C=N] (1c). Synthesis of 1c was conducted similarly as that for 1a, except that Cp*TiCl₃ (540 mg, 1.87 mmol), 1,3-(C₆H₅)₂(CH₂N)₂C=NH (443 mg, 1.87 mmol) and 1 equiv. of ⁿBuLi (1.87 mmol, 1.6 M in n-hexane) were used. After the similar purification procedure, orange microcrystals were obtained from the chilled solution (−30 °C). Yield 440 mg (48%). ¹H NMR (CDCl₃): δ 1.63 (s, 15H, C₅Me₅), 4.09 (s, 4H, NCH₂CH₂N), 7.14 (t, 2H, p-C₆H₅), 7.36 (t, 4H, m-C₆H₅), 7.54 (d, 4H, o-C₆H₅). ¹³C NMR (CDCl₃): δ 12.4 (C₅Me₅), 46.0 (NCH₂CH₂N), 123.5 (Ph), 125.4 (Ph), 127.3 (C₅Me₅), 129.3 (Ph), 138.5 (Ph), 151.0 (N₂CN) Anal. calcd for C_25.1H_29.2Cl_2.2N₃Ti: C, 60.44; H, 5.90; N, 8.42%. Found: C, 60.24; H, 5.67; N, 8.29%. The resultant microcrystals of 1c contain CH₂Cl₂ even after placing in vacuo for long hours.

Synthesis of Cp*TiCl₂[1,3-(2,6-Me₂C₆H₃)₂(CH₂N)₂C=N] (1d). Synthesis of 1d was conducted similarly as that for 1a, except that Cp*TiCl₃ (540 mg, 1.87 mmol), 1,3-(2,6-Me₂C₆H₃)₂(CH₂N)₂C=NH (549 mg, 1.87 mmol) and 1 equiv. of ⁿBuLi (1.87 mmol, 1.6 M in n-hexane) were used. After the similar purification procedure, yellow microcrystals were obtained from the chilled solution (−30 °C). Yield 591 mg (58%). ¹H NMR (CDCl₃): δ 1.19 (s, 15H, C₅Me₅), 2.48 (s, 12H, Me₂Ph), 3.92 (s, 4H, NCH₂CH₂N), 7.09 (m, 6H, Me₂Ph). ¹³C NMR (CDCl₃): δ 12.3 (C₅Me₅), 18.7 (Me₂Ph), 46.0 (NCH₂CH₂N), 126.6 (C₅Me₅), 128.4 (Ph), 135.4 (Ph), 137.0 (Ph), 137.7 (Ph), 149.9 (N₂CN). Anal. calcd for C_31.1H_39.4Cl₂N₃Ti: C, 65.07; H, 6.92; N, 7.32%. Found: C, 64.30; H, 6.98; N, 7.29%. The resultant microcrystals of 1d contain toluene even after placing in vacuo for long hours (as seen in the crystallographic analysis).

Synthesis of Cp*TiCl₂[1,3-(2,6-ⁱPr₂C₆H₃)₂(CH₂N)₂C=N] (1e). Synthesis of 1e was conducted similarly as that for 1a, except that Cp*TiCl₃ (579 mg, 2.00 mmol), 1,3-(2,6-ⁱPr₂C₆H₃)₂(CH₂N)₂C=NH (475 mg, 2.00 mmol) and 1 equiv. of ⁿBuLi (2.00 mmol, 1.6 M in n-hexane) were used. After the similar purification procedure, yellow microcrystals were obtained from the chilled solution (−30 °C). Yield 1120 mg (85%). ¹H NMR (CDCl₃): δ 1.27 (d, 12H, ⁱPr₂Ph), 1.45 (d, 12H, ⁱPr₂Ph), 1.72 (s, 15H, C₅Me₅), 3.34 (m, 4H, Me₂CH), 3.93 (s, 4H, NCH₂CH₂N), 7.22 (d, 4H, m-ⁱPr₂Ph), 7.35 (t, 2H, p-ⁱPr₂Ph). ¹³C NMR (CDCl₃): δ 12.7 (C₅Me₅), 23.7 (ⁱPr₂Ph), 26.2 (ⁱPr₂Ph), 28.9 (ⁱPr₂Ph), 49.4 (NCH₂CH₂N), 124.5 (Ph), 127.1 (C₅Me₅), 129.2 (Ph), 134.5 (Ph), 147.9 (Ph), 150.6 (CNH). Anal. calcd for C₃₇H₅₃Cl₂N₃Ti: C, 67.47; H, 8.11; N, 6.38%. Found: C, 67.23; H, 8.10; N, 6.35%.

Ethylene polymerisation, ethylene/1-hexene copolymerisation, ethylene/styrene copolymerisation, and ethylene/norbornene copolymerisation. Ethylene polymerisations were conducted in toluene by using a 100 mL scale autoclave. Solvent (29.0 mL) and prescribed amount of d-MAO white solid, prepared by removing toluene and AlMe₃ from commercially available MAO (PMAO-S, Tosoh Finechem Co.), were charged into the autoclave in the drybox, and the apparatus was placed under ethylene atmosphere (1 atm). After the addition of a toluene solution (1.0 mL) containing a prescribed amount of complex via a syringe, the reaction apparatus was pressurised to 5 atm (total 6 atm), and the mixture was stirred magnetically for 10 min. After the above procedure, ethylene was purged, and the mixture was then poured into MeOH (150 mL) containing HCl (10 mL). The resultant polymer was collected on a filter paper by filtration and was adequately washed with MeOH and then dried in vacuo. Experimental procedures for the ethylene/1-hexene copolymerisations were the same as those for the ethylene polymerisations except that a prescribed amount of 1-hexene (5.0 mL) was charged and the total volume of toluene and 1-hexene was set to 30 mL. Experimental procedures for the ethylene/styrene, ethylene/norbornene copolymerisations were the same as those for the ethylene polymerisations except that a prescribed amount of norbornene or styrene was charged and the total volume of toluene was set to 30 mL.

Crystallographic analysis

All measurements were made on a Rigaku RAXIS-RAPID Imaging Plate Diffractometer with graphite monochromated Mo-Kα radiation. The selected crystal collection parameters are listed in Table 9, and the detailed results were described in the reports in the ESI.† All structures were solved by direct methods²² and expanded using Fourier techniques (except for 1b),²³ and the non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included but not refined. All calculations were performed using the crystal structure²⁴ crystallographic software package except for refinement, which was performed using SHELXL-97.²⁵ Detailed analysis data including the collection parameters, CIF files, and the structure reports are shown in the ESI.†

Table 9 Crystal data and collection parameters of Cp*TiCl₂[1,3-(2,6-R₂C₆H₃)₂(CH₂N)₂C=N] [R = Cy (1b), C₆H₅ (1c), 2,6-Me₂C₆H₃ (1d), 2,6-ⁱPr₂C₆H₃ (1e)]^a

	1b	1c	1d^b	1e^b
a ESI.b Crystals contain CH2Cl2, detailed data can be seen in ESI.
Formula	C25H41Cl2N3Ti	C25H29Cl2N3Ti	C117H148Cl10N12Ti4	C39H53Cl6N3Ti
Formula weight	502.42	490.33	2268.67	824.49
Crystal color, habit	Yellow, block	Yellow, block	Yellow, block	Yellow, block
Crystal size (mm)	0.65 × 0.55 × 0.40	0.15 × 0.12 × 0.06	0.62 × 0.20 × 0.18	0.20 × 0.16 × 0.10
Crystal system	Monoclinic	Monoclinic	Orthorhombic	Triclinic
Space group	P21/c (#14)	P21/n (#14)	P21212 (#18)	P1̄ (#2)
a (Å)	8.5977(3)	8.6563(3)	21.8842(5)	11.1642(2)
b (Å)	15.5686(4)	7.4257(2)	28.7235(7)	11.2931(2)
c (Å)	20.0179(6)	36.557(1)	9.4156(2)	19.4433(4)
β (deg)	103.7144(8)	94.0965(9)		100.1681(7)
V (Å^3)	2603.07(13)	2343.9(1)	5918.6(3)	2151.93(7)
Z value	4	4	2	2
Dcalcd (g cm^−3)	1.282	1.389	1.273	1.272
F000	1072.00	1024.00	2384.00	864.00
Temp. (K)	123	123	213	123
μ (MoKα) (cm^−1)	5.512	6.108	5.368	6.007
No. of reflections measured	25 348	22 274	58 490	37 405
No. of observations (I > 2.00σ(I))	5923	5362	13 519	9868
No. of variables	281	280	643	511
R1(I > 2.00σ(I))	0.0331	0.0390	0.0366	0.0453
wR2 (I > 2.00σ(I))	0.0750	0.0968	0.0971	0.1224
Goodness of fit	1.095	1.203	1.047	1.142

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Acknowledgements

The present research is partly supported by Grant-in-Aid for Scientific Research (B) from the Japan Society for the Promotion of Science (JSPS, No. 24350049, 15H03812). The project was partly supported by the advanced research program (Tokyo metropolitan government), and S. P. expresses her thanks to Tokyo metropolitan government (Asian Human Resources Fund) for pre-doctoral fellowship. The authors also express their thanks to Tosoh Finechem Co. for donating MAO (TMAO). S. P. and K. N. express their heartfelt thanks to Profs A. Inagaki and S. Komiya (Tokyo Metropolitan University) for fruitful discussion. K. N. also acknowledges to Japan Polychem Corp. for some GPC analyses.

Notes and references

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13. The results are partly introduced at Chemelot International Polyolefins Symposium (CIPS2012, Maastricht, The Netherland, October, 2012); International Symposium on Relations between Homogeneous and Heterogeneous Catalysis (ISHHC-16) Sapporo, August, 2013.
14. ESI†.
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Footnote

† Electronic supplementary information (ESI) available: Structure reports for complexes 1b–e. CCDC 1403201–1403204. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5ra11402k

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