Synthesis, characterization, and the ethylene (co-)polymerization behaviour of half-titanocene dichloride 2-aryliminoquinolin-8-olates

Abstract

A series of half-titanocene dichloride 2-aryliminoquinolin-8-olates, CpTi LCl₂ (C1–C6: Cp as C₅H₅, L as 2-(1-(o-benzhydrylarylimino)methyl)quinolin-8-olates or 2-(1-(o-benzhydrylarylimino)ethyl)quinolin-8-olates), was synthesized and fully characterized; the molecular structures of representative complexes C2 and C4 are reported. Upon activation with modified methylaluminoxane (MMAO), the title complexes exhibited good activities for ethylene polymerization (up to 1.56 × 10⁶ g mol⁻¹ (Ti) h⁻¹). The C4/MMAO system was further investigated for the co-polymerization of ethylene with 1-hexene, 1-octene, or isoprene.

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Introduction

Metallocene complexes were used as model pre-catalysts in understanding the mechanism of Ziegler–Natta type catalysis in the 1950s.¹ Further dramatic developments in the 1980s were initiated following the discovery that highly active catalytic metallocene systems were accessible upon activation with the co-catalyst methylaluminoxane (MAO).^2,3 Subsequent studies revealed how metallocene pre-catalysts could be finely tuned, characteristically producing polyolefins with narrow molecular weight distributions and desirable microstructures.^4–7 Moreover, bridged half-metallocene pre-catalysts (constrained geometry catalysts, CGCs), were developed for industrial processes by the Dow and Exxon Chemical companies.^8–13 Problems associated with CGCs still remain, in-particular, there are only a limited number of alternative (and useful) ligand types available, and synthetic problems relating to both yield and cost still persist. To overcome the shortfall in available ligand sets, non-bridged half-metallocene pre-catalysts were designed, and included various modifications of the anionic ligands. Both high activity and precise control over co-polymerization ability were accomplished.^14–17 The anionic ligands deployed could be classified as mono-dentate such as aryloxy^18,19 or ketimide,²⁰ bi-dentate such as acetamidinato,^21–24 iminophenoxy,^25,26 pyridinylalkyloxy,²⁷ and N-substituted (iminomethyl) pyrrolides,^28,29 as well as multi-dentate such as β-ketoimine.^30,31 More recently, titanium-based catalytic systems such as the FI catalysts employing iminophenolates^32–38 and PI catalysts containing iminopyrrolide have been developed.^39–42 The non-bridged half-metallocene pre-catalysts showed high activities for co-polymerizations,^{17–19,43–46} and we recently reported half-titanocene chloride complexes bearing anionic multidentate ligands, which exhibited both good stability and activity.^47–51 The ligand family 2-(1-(arylimino)alkyl)quinolin-8-olates were used in preparing aluminium pre-catalysts for the ring-opening polymerization of ε-caprolactone,⁵² and were also used to prepare trichlorotitanium,⁵³ half-titanocene chloride,^54,55 and zirconium complexes,⁵⁶ which acted as highly active pre-catalysts for ethylene homo-polymerization and co-polymerization. Within the catalytic system comprising half-titanocene dichloride 2-(1-(arylimino)alkyl)quinolin-8-olates,^54,55 the longer the side-chain in the ligand, the higher the catalytic activity observed, i.e. pre-catalysts using the 2-(1-(arylimino)propyl)quinolin-8-olate ligand set⁵⁴ exhibited higher activities than did those bearing 2-(1-(arylimino)ethyl)quinolin-8-olates.⁵⁵ Given this, it would be interesting to examine the different catalytic behavior of half-titanocene pre-catalysts bearing 2-aldiminoquinolin-8-olates versus 2-ketiminoquinolin-8-olates. Furthermore, bulky substituents at the aryl_imino group of ligands derived from such aldimine/ketimine systems are very likely to influence the catalytic activities of the resultant complexes. Thus, bulky ligands derived from 2-(1-(o-benzhydrylarylimino)alkyl)quinolin-8-ol were prepared via the condensation reaction of o-benzhydrylanilines with either 8-hydroxyquinoline-2-carbaldehyde or 1-(8-hydroxy-quinolin-2-yl)ethanone. On further reaction with CpTiCl₃, the title half-titanocene complexes were prepared. Catalytic screening revealed good activities for ethylene homo-polymerization and co-polymerization with 1-hexene, 1-octene or isoprene. Herein, the synthesis and characterization of the title complexes as well as their catalytic behavior are reported.

Results and discussion

Synthesis and characterization

The stoichiometric reaction of CpTiCl₃ with the corresponding potassium 2-aryliminoquinolin-8-olate in toluene, afforded the (η⁵-cyclopentadienyl)titanium dichloride 2-(1-(o-benzhydrylaryl-imino)alkyl)quinolin-8-olates (C1–C6; Scheme 1) in good yields (55–80%).

Scheme 1 Synthesis of titanium complexes C1–C6.

Successful complexation resulting in the formation of Ti–O bonds could be followed by either FT-IR or ¹H NMR spectroscopy; all complexes possessed a lack of bands at about 3410 cm⁻¹ in their IR spectra and the peak at ca. 8.07 ppm in the ¹H NMR spectra of the parent ligands. Furthermore, in the ¹³C NMR spectra there was a 3–5 ppm downfield shift of the resonances associated with the CH=N functionality in complexes C1–C3 when compared to those observed for the parent ligands L1–L3 (164–165 ppm), whilst there was a 1–3 ppm downfield shift for CCH₃=N in the complexes C4–C6cf. to the ligands L4–L6 (168–169 ppm). Elemental analytical data were consistent with complexes of molecular formula CpTiLCl₂. Representative molecular structures were confirmed for complexes C2 and C4via single crystal X-ray diffraction.

X-ray crystallographic studies

As shown in Fig. 1, complex C2 contains one chelating ligand, together with a Cp ring and two chlorides, all of which form a pseudo octahedral geometry at the titanium centre. The distance between the centroid of the Cp ring and the titanium atom is 2.075 Å, whilst the Ti1–C bond lengths are slightly different with a range of 2.371 Å to 2.401 Å (ΔTi–C = 0.03 Å); the carbons (C44, C45, C46, C47, and C48) are coplanar. The tridentate N⁁N⁁O ligand coordinated with titanium in a meridianal manner, and the two chlorides located in trans-form with the Cl1–Ti1–Cl2 as 151.92(7)°. The Ti–Cl bond lengths are slightly different at around 2.43 Å, whilst the Ti1–O1 bond length is 1.959 Å, consistent with observations for analogous complexes.^54,55 Selected bonds and angles are tabulated in Table 1.

Fig. 1 ORTEP drawing of complex C2 with thermal ellipsoids at 30% probability level. Hydrogen atoms have been omitted for clarity.

Table 1 Selected bond lengths (Å) and angles (°) for C2 and C4

	C2	C4
Bond lengths (Å)
Ti1–O1	1.959(4)	1.948(4)
Ti1–N1	2.131(5)	2.127(5)
Ti1–N2	2.372(5)	2.402(5)
Ti1–Cl1	2.4398(19)	2.4528(19)
Ti1–Cl2	2.4331(19)	2.4518(18)
Ti1–Cpcent	2.075	2.078
Bond angles (°)
O1–Ti1–N1	77.45(18)	77.47(19)
O1–Ti1–N2	146.62(17)	146.09(18)
N1–Ti1–N2	69.17(16)	68.62(17)
O1–Ti1–Cl1	87.85(13)	88.99(14)
N1–Ti1–Cl1	75.70(13)	75.26(14)
N2–Ti1–Cl1	84.28(12)	83.04(12)
O1–Ti1–Cl2	87.74(14)	86.16(14)
N1–Ti1–Cl2	76.27(13)	76.52(14)
N2–Ti1–Cl2	84.28(12)	85.60(12)
Cl1–Ti1–Cl2	151.92(7)	151.75(7)
Cpcent–Ti1–N1	177.08	177.29
Cpcent–Ti1–N2	107.98	108.67
Cpcent–Ti1–O1	105.40	105.23
Cpcent–Ti1–Cl1	103.60	104.59
Cpcent–Ti1–Cl2	104.31	103.53

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There are only slight structural differences between C2 and complex C4 (Fig. 2). The dihedral angle defined by the two chelating rings ΘTi1–O1–C1–C6–N1 and ΘTi1–N1–C9–C10–N2 is 2.98° for C4, slightly larger than the corresponding dihedral angle in C2 (1.75°).

Fig. 2 ORTEP drawing of the molecular structure of C4 (ellipsoids enclose 30% electronic density; H atoms are omitted for clarity).

Ethylene polymerization

The pre-catalyst C1 was screened to find the most suitable co-catalyst and optimum catalytic conditions. Employing alkylaluminum co-catalysts such as AlMe₃, AlEt₃, EtAlCl₂, and Et₂AlCl, only negligible activity was observed. However, pre-catalyst C1 showed good activity for ethylene polymerization when using either MAO or MMAO as co-catalyst. On fixing the molar Al/Ti ratio at 3000 : 1 at a temperature of 60 °C over 30 min at 10 atm, the activity was observed to be 1.9 × 10⁵ g mol⁻¹ (Ti) h⁻¹ in the presence of MAO, and 6.1 × 10⁵ g mol⁻¹ (Ti) h⁻¹ when using MMAO. Given these results, further investigations were conducted using MMAO as co-catalyst.

To find the most suitable Al/Ti molar ratio, trials with varying Al/Ti molar ratios, from 2000 to 7000 : 1, were conducted at 60 °C over 30 min (Runs 2–7, Table 2), which indicated that the highest activity (9.4 × 10⁵ g mol⁻¹ (Ti) h⁻¹) was achieved at an Al/Ti ratio of 5000 : 1. GPC measurements showed that the obtained polyethylenes had lower molecular weights on increasing the molar ratio of Al/Ti (Fig. 3), consistent with the explanation that a higher Al/Ti molar ratio enhances chain transfer to aluminium, i e. termination.^57,58

Fig. 3 GPC profiles of PEs obtained from Runs 3–7 in Table 2.

Table 2 Ethylene polymerization using C1 with MAO or MMAO^a

Run	Co-cat	t/min	Al/Ti	T/°C	Polym/g	Act^b	T m ^c/°C	M w ^d ^, ^e	M w/Mn^e
a Conditions: 1 μmol complex C1, toluene (total volume 100 mL), 10 atm. b 10^5 g mol^−1 (Ti) h^−1. c Determined by DSC. d 10^4 g mol^−1. e Determined by GPC.
1	MAO	30	3000	60	0.095	1.90	134.7	74.1	6.17
2	MMAO	30	3000	60	0.305	6.10	135.3	74.7	2.82
3	MMAO	30	2000	60	0.230	4.60	135.4	76.2	3.27
4	MMAO	30	4000	60	0.270	5.40	134.3	74.9	2.94
5	MMAO	30	5000	60	0.470	9.40	135.0	70.1	1.93
6	MMAO	30	6000	60	0.397	7.94	135.1	61.6	2.84
7	MMAO	30	7000	60	0.282	5.64	130.2	58.9	2.06
8	MMAO	20	5000	60	0.181	5.43	130.0	58.1	3.09
9	MMAO	10	5000	60	0.124	7.44	129.5	57.8	2.38
10	MMAO	30	5000	50	0.196	3.92	135.0	78.8	2.68
11	MMAO	30	5000	70	0.346	6.92	133.9	65.7	2.10
12	MMAO	30	5000	80	0.220	4.40	134.2	63.2	2.54

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With regard to the reaction temperature (runs 5, 10–12, Table 2), the optimum temperature was found to be 60 °C, for which the activity was 9.4 × 10⁵ g mol⁻¹ (Ti) h⁻¹. The higher the reaction temperature, the lower the concentration of ethylene in solution, and therefore the lower the activity observed. The molecular weights of the obtained polyethylenes decreased on elevating the temperature (Fig. 4); i.e., faster chain terminations at elevated temperatures. These trends are consistent with those observed for related titanium complexes⁵⁵ and other half-titanocene pre-catalysts.⁴⁸

Fig. 4 GPC profiles of PEs obtained from Runs 5 and 10–12 in Table 2.

Over different reaction periods of 10, 20, and 30 min (Runs 5, 8, and 9, Table 2), the highest activity was observed at 30 min, indicative of a rather stable species for this catalytic system; meanwhile the slightly lower activity value for 20 min (Run 8) indicated the induction period required to form active species in the current catalytic system. As indicated by their GPC curves, some polyethylene of lower molecular weight was formed in a short reaction time (Fig. 5). On prolonging the reaction time, the obtained polyethylene possessed higher molecular weight and narrower molecular distribution. When compared to the analogous half-titanocene dichloride 2-(1-(arylimino)ethyl)quinolin-8-olates,⁵⁵ lower activity was observed, and higher molecular weights and narrower molecular distributions for the polyethylenes were obtained. It is thought that the bulky ligand present prevented the coordination of ethylene and protected the active species in this catalytic system.

Fig. 5 GPC profiles of PEs obtained from Runs 5, 8 and 9 in Table 2.

Using the optimum conditions of Al/Ti ratio of 5000 : 1 at 60 °C under 10 atm over 30 min, all the pre-catalysts C1–C6 were screened for ethylene polymerization (Table 3). The bulkier the ligand used, the lower the activity observed, thus C1 (R¹ = Me, R² = Ph₂CH) > C2 (R¹ = R² = Ph₂CH), C4 (R¹ = Me, R² = Ph₂CH) > C5 (R¹ = R² = Ph₂CH), consistent with bulkier ortho-substituents at the aryl_imino group preventing access of ethylene to the active centre. For the same ortho-substituent at the aryl_imino group, pre-catalysts possessing a para-isopropyl substituent at the aryl_imino showed higher activity than did analogues possessing a para-methyl substituent at the aryl_imino group, i e.C3 (R³ = i-Pr, R¹ = R² = Ph₂CH) > C2 (R³ = Me, R¹ = R² = Ph₂CH) and C6 (R³ = i-Pr, R¹ = R² = Ph₂CH) > C5 (R³ = Me, R¹ = R² = Ph₂CH), indicating the better activity was caused by the better soluble para-isopropyl group. In addition, better catalytic activities were observed for the ketimine systems versus the aldimines, i e.C4 (R = Me) > C1 (R = H), C5 (R = Me) > C2 (R = H), C6 (R = Me) > C3 (R = H). These were consistent with our previous observations for half-titanocene dichloride 2-aryliminoquinolin-8-olates, where higher activities were achieved by 2-(1-(arylimino)propyl)quinolin-8-olates⁵⁴ over 2-(1-(arylimino)ethyl)quinolin-8-olates.⁵⁵ Besides the better solubility of the complexes bearing ligands with longer alkyl groups, the longer chain alkyl substituents can also be considered better electron-donors capable of stabilizing electron-deficient titanium complexes.^59,60

Table 3 Ethylene polymerization by the C1–C6/MMAO system^a

Run	Cat	Polym/g	Act^b	T m ^c/°C	M w ^d ^, ^e	M w/Mn^e
a Conditions: 1 μmol complexes, toluene (total volume 100 mL), Al/Ti = 5000, 30 min, 60 °C, 10 atm. b 10^5 g mol^−1 (Ti) h^−1. c Determined by DSC. d 10^4 g mol^−1. e Determined by GPC.
1	C1	0.470	9.40	135.0	70.1	1.93
2	C2	0.430	8.60	122.2	44.5	3.68
3	C3	0.463	9.26	130.3	38.8	3.03
4	C4	0.780	15.6	135.0	65.4	2.00
5	C5	0.585	11.7	130.8	62.5	3.26
6	C6	0.612	12.2	125.9	49.7	2.44

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Ethylene co-polymerization

The co-polymerization of ethylene with 1-hexene was investigated using the pre-catalyst C4 and employing the optimum conditions determined for ethylene homo-polymerization, i.e. Al/Ti ratio at 5000 : 1 at 60 °C over 30 min under 10 atm of ethylene, whilst at the same time changing the concentration of 1-hexene (Table 4). A positive effect of the co-monomer was observed, leading to better activities for the co-polymerization than for ethylene homo-polymerization. However, the catalytic activities decreased with increasing co-monomer concentration (runs 1–3, Table 4), consistent with the observations for half-titanocene pre-catalysts featuring amidate⁴⁸ or imino-indolate ligands.⁵¹ GPC analysis showed that the molecular weights of the obtained polymers decreased with increasing concentration of 1-hexene, suggesting possibly that chain termination occurred during the insertion of co-monomer. According to DSC analysis, the melting points of the obtained polymers were lower, indicating more branching on increasing the concentration of 1-hexene. Similar catalytic tendencies were also observed for the ethylene/1-octene co-polymerization (Table 4), though the activities for 1-octene were slightly lower than those observed for 1-hexene.

Table 4 Ethylene/1-olefin co-polymerization by the C4/MMAO system^a

Run	Monomer	Polym/g	Act^b	T m ^c/°C	M w ^d ^, ^e	M w/Mn^e
a Conditions: 1 μmol complex C4, toluene (total volume 100 mL), Al/Ti = 5000, 30 min, 60 °C, 10 atm. b 10^5 g mol^−1 (Ti) h^−1. c Determined by DSC. d 10^4 g mol^−1. e Determined by GPC.
1	0.4 M C6^=	0.568	11.4	125.3	60.0	2.32
2	0.7 M C6^=	0.43	8.60	116.4	45.5	2.79
3	1 M C6^=	0.23	4.60	103.2	18.9	2.65
4	0.4 M C8^=	0.308	6.16	122.8	50.0	3.49
5	0.7 M C8^=	0.256	5.12	116.3	44.9	3.25
6	1 M C8^=	0.177	3.54	101.2	11.3	11.9

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The ¹³C NMR spectrum (Fig. 6) of the ethylene/1-hexene co-polymer indicated a 3.39 mol% incorporation of 1-hexene in the resultant polymer (Run 2, Table 4). The 1-hexene incorporation ability herein was lower than other similar half-titanocenes,^54,55 indicating that the bulky ligand probably prevented the insertion of the 1-hexene monomer. The ¹³C NMR spectrum was assigned according to the literature.⁶¹ Meanwhile the ¹³C NMR spectrum (Fig. 7) of the ethylene/1-octene co-polymer indicated a 3.22 mol% incorporation of 1-octene (Run 5, Table 4).

Fig. 6 ¹³C NMR spectrum of the ethylene/1-hexene co-polymer.

Fig. 7 ¹³C NMR spectrum of the ethylene/1-octene co-polymer.

Moreover, co-polymerization of ethylene with isoprene was also conducted using the C4/MMAO system (Table 5), and it was observed that the activities of the co-polymerization slowly decreased on increasing the concentration of isoprene, which was in contrast with previous reports in the literature.⁶² The molecular weights of ethylene-isoprene co-polymers decreased on increasing the monomer concentration, which was consistent with the above co-polymerizations with 1-hexene or 1-octene.

Table 5 Ethylene/Isoprene co-polymerization by the C4/MMAO system^a

Run	Concentration	Polym/g	Act^b	T m ^c/°C	M w ^d ^, ^e	M w/Mn^e
a Conditions: 1 μmol complex C4, toluene (total volume 100 mL), Al/Ti = 5000, 30 min, 60 °C, 10 atm. b 10^5 g mol^−1 (Ti) h^−1. c Determined by DSC. d 10^4 g mol^−1. e Determined by GPC. n.d.: polymer partly unsolvable.
1	0.4 M	0.697	13.9	134.2	63.2	2.24
2	0.7 M	0.509	10.2	133.9	33.6	2.84
3	1 M	0.394	7.88	133.0	n.d.	n.d.

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The ¹³C NMR spectra (Fig. 8) of the co-polymer (Run 2, Table 5) indicated a random co-polymer containing mainly PE units, and cis-1,4-IP-alt-E sequences with small amounts of trans-1,4-IP-alt-E (cis : trans = 75.8% : 25.2%), without 2-IP-alt-E or 3,4-IP-alt-E units.

Fig. 8 ¹³C NMR spectrum of the ethylene/isoprene co-polymer.

The monomer compositions were illustrated by comparing the integrals of the ¹H NMR spectra (Fig. 9) by using the following formula (eqn (1)) according to the literature.⁶³

Fig. 9 ¹H NMR spectrum of the ethylene/isoprene co-polymer.

Mol IP% = {(I_H1 + 0.5I_H2)/(I_H1 + 0.5I_H2 + 0.25(I_H5 − I_H2))} × 100 (1)

in which I_H1 is the integration of the resonance at 5.13 ppm (one vinyl proton of the 1,4-isoprene unit), I_H2 is the integration of the resonance at 4.72 ppm (two vinyl protons of the 3,4-isoprene unit) in the ¹H NMR spectrum, and I_H5 is the integration of the broad signals at 1.3 ppm as the total methylene protons in both 3,4-isoprene units and ethylene units in the ¹H NMR spectrum. The ¹H NMR spectrum indicated a 1.75 mol% isoprene incorporation in the resultant polymer (Run 2, Table 5).

Conclusion

A series of half-titanocene dichloride 2-(o-benzhydrylaryl- imino)quinolin-8-olates was synthesized and fully characterized. All half-titanocene complexes showed good activities for ethylene polymerization using MMAO as co-catalyst. The bulky ortho-substituents of the aryl_imino group prevented access of ethylene to the active titanium centre, thereby resulting in the lower observed activity. Longer chain alkyl-substituents (R and R³) enhanced the solubility of the complexes and resulted in better observed activity. The positive effect of the co-monomer was observed in the co-polymerization, however, the catalytic activities decreased with higher co-monomer concentrations. Comparison to the related half-titanocene^54,55 and CGC pre-catalysts,^8,9 the current system showed a better thermo-stability for ethylene polymerization, and also good activity toward ethylene/isoprene copolymerization.

Experimental section

General considerations

All manipulations of air and/or moisture-sensitive compounds were performed under nitrogen atmosphere in a glove-box or using standard Schlenk techniques. Methylaluminoxane (MAO, 1.46 M in toluene) was purchased from Albemarle and other reagents were purchased from Aldrich or Acros Chemicals. Modified methylaluminoxane (MMAO, 1.93 M in heptane) was purchased from Akzo Nobel Corp. Potassium hydride (KH), purchased from Beijing Regent Chemicals, was washed with hexane before use to remove contained mineral oil. Toluene, n-hexane, n-heptane and isoprene were refluxed over sodium and benzophenone, distilled, and then stored over activated molecular sieves (4 Å) for 24 h under nitrogen atmosphere. Dichloromethane (CH₂Cl₂), 1-hexene, and 1-octene were refluxed over calcium hydride, distilled, and then stored over activated molecular sieves (4 Å) for 24 h in a glove-box prior to use. CDCl₃ was dried over activated 4 Å molecular sieves. IR spectra were recorded on a Perkin Elmer FT-IR 2000 spectrometer using a KBr disc in the range of 4000–400 cm⁻¹. Elemental analysis was performed on a Flash EA 1112 microanalyzer. ¹H NMR and ¹³C NMR spectra were recorded on a Bruker DMX 400 MHz instrument at ambient temperature using TMS as an internal standard. Assignments are based on COSY, HSQC and HMBC experiments. DSC trace and melting points of polyethylene were obtained from the second scanning run on a Perkin-Elmer DSC-7 at a heating rate of 10 °C min⁻¹. ¹³C NMR spectra of the polymers were recorded on a Bruker DMX-300 MHz instrument at 112 °C in deuterated 1,2-dichlorobenzene with TMS as an internal standard. The molecular weight and molecular weight distribution of the polymers were determined by gel permeation chromatography (GPC) using a Waters Alliance GPC 2000 instrument equipped with a refractive index (RI) detector and a set of u-Styragel HT columns of 10⁶, 10⁵, 10⁴, and 10³ pore size in series. The measurement was performed at 150 °C with 1,2,4-trichlorobenzene as the eluent at a flow rate of 0.95 mL min⁻¹. Narrow-molecular-weight PS samples were used as standards for calibration.

Synthesis of 2-((2-benzhydryl-4,6-dimethylphenylimino)methyl)quinolin-8-ol (L1)

A solution of 2-benzhydryl-4,6-dimethylbenzenamine (0.689 g, 2.4 mmol) and 8-hydroxyquinoline-2-carbaldehyde (0.346 g, 2 mmol) in ethanol was refluxed for 12 h, then the solvent was removed in vacuo. The product, 2-((2-benzhydryl-4,6-dimethylphenylimino)methyl)quinolin-8-ol (L1), was purified by column chromatography (silica gel, petroleum ether/ethyl acetate = 10 : 1), the second part to elute was collected and concentrated to give a yellow green solid in 69.1% yield (0.63 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.29–8.21 (m, 2H), 8.02 (s, 1H), 7.84 (s, 1H), 7.51 (t, J = 7.9 Hz, 1H), 7.37 (d, J = 8.1 Hz, 1H), 7.23–7.05 (m, 7H), 7.04 (d, J = 6.8 Hz, 4H), 6.98 (s, 1H), 6.63 (s, 1H), 5.57 (s, 1H), 2.25 (s, 3H), 2.14 (s, 3H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 164.3, 152.6, 152.1, 147.8, 143.8, 137.7, 136.7, 134.1, 133.4, 129.9, 129.8, 129.7, 129.2, 129.1, 128.6, 128.3, 128.2, 126.2, 126.0, 118.8, 117.9, 110.5, 52.3, 21.2, 18.4. IR (KBr, cm⁻¹): 3410 (m), 2916 (w), 1974 (w), 1636 (m), 1561 (m), 1503 (m), 1469 (s), 1363 (s), 1329 (m), 1299 (m), 1237 (s), 1202 (m), 1135 (m), 1103 (m), 1036 (m), 846 (s), 793 (m), 745 (s), 697 (s). Mp: 88–89 °C. Anal. Calcd. For C₃₁H₂₆N₂O: C, 84.13; H, 5.92; N, 6.33. Found: C, 84.11; H, 5.98; N, 6.29.

2-(1-(2,6-dibenzhydryl-4-methylphenylimino)methyl)quinolin-8-ol (L2)

Using the above procedure, but 2,6-dibenzhydryl-4-methyl-benzenamine was used instead of 2-benzhydryl-4,6-dimethyl-benzenamine, the 2-(1-(2,6-dibenzhydryl-4-methylphenylimino) methyl)quinolin-8-ol (L2) was obtained as a yellow green solid in 72.4% yield (0.88 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.16 (d, J = 8.1 Hz, 1H), 8.08 (d, J = 8.3 Hz, 1H), 7.85 (s, 1H), 7.48 (t, J = 7.6 Hz, 1H), 7.33 (d, J = 7.9 Hz, 1H), 7.25–7.11 (m, 14H), 7.02 (d, J = 6.0 Hz, 8H), 6.68 (s, 2H), 5.45 (s, 2H), 2.17 (s, 3H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 165.5, 152.7, 151.7, 147.9, 143.8, 142.9, 136.5, 133.2, 132.9, 129.8, 129.7, 129.4, 129.2, 129.1, 128.6, 128.4, 126.7, 126.3, 118.8, 117.9, 110.4, 52.5, 21.5. IR (K Br, cm⁻¹): 3411 (m), 3021 (w), 2166 (w), 2029 (w), 1636 (m), 1598 (m), 1565 (m), 1508 (m), 1493 (s), 1471 (m), 1444 (m), 1327 (m), 1239 (s), 1202 (m), 1078 (m), 1032 (m), 915 (m), 839 (s), 757 (m), 739 (s), 697 (s). Mp: 99–101 °C. Anal. Calcd. For C₄₃H₃₄N₂O: C, 86.84; H, 5.76; N, 4.71. Found: C, 86.81; H, 5.78; N, 4.68.

2-(1-(2,6-dibenzhydryl-4-isopropylphenylimino)methyl)quinolin-8-ol (L3)

Similarly, the 2-(1-(2,6-dibenzhydryl-4-isopropylphenylimino)methyl)quinolin-8-ol (L3) was obtained as a yellow green solid in 81.8% yield (1.04 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.16 (d, J = 8.6 Hz, 1H), 8.07 (d, J = 8.6 Hz, 1H), 7.85 (s, 1H), 7.48 (t, J = 7.9 Hz, 1H), 7.34 (d, J = 8.2 Hz, 1H), 7.24–7.12 (m, 14H), 7.00 (d, J = 7.1 Hz, 8H), 6.72 (s, 2H), 5.45 (s, 2H), 2.74–2.67 (m, 1H), 1.05 (d, J = 6.9 Hz, 6H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 165.1, 152.7, 151.7, 148.1, 143.9, 137.6, 136.5, 133.1, 129.8, 129.2, 128.3, 126.4, 126.3, 118.9, 117.8, 110.4, 52.4, 33.7, 24.1. IR (KBr, cm⁻¹): 3382 (w), 3025 (w), 2959 (w), 1632 (m), 1600 (m), 1569 (m), 1508 (m), 1493 (s), 1445 (s), 1371 (m), 1327 (m), 1287 (m), 1235 (s), 1199 (m), 1077 (m), 1030 (m), 841 (m), 738 (s), 696 (s). Mp: 101–102 °C. Anal. Calcd. For C₄₅H₃₈N₂O: C, 86.78; H, 6.15; N, 4.50. Found: C, 86.74; H, 6.11; N, 4.53.

2-(1-(2-benzhydryl-4,6-dimethylphenylimino)ethyl)quinolin-8-ol (L4)

The mixture of 0.374 g (2.0 mmol) 1-(8-hydroxyquinolin-2-yl)ethanone, (0.689 g, 2.4 mmol) 2-benzhydryl-4,6-dimethyl-benzenamine and a catalytic amount of p-toluenesulfonic acid (0.10 g) in 20 m L toluene was refluxed for 24 h. After toluene evaporation, 2-(1-(2-benzhydryl-4,6-dimethylphenylimino)ethyl)quinolin-8-ol (L4) was purified on column chromatography (silica gel, petroleum ether/ethyl acetate = 20 : 1) and obtained as a yellow green solid in 46.1% (0.42 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.48 (d, J = 8.6 Hz, 1H), 8.23 (d, J = 8.6 Hz, 1H), 8.07 (s, 1H), 7.51 (t, J = 7.9 Hz, 1H), 7.39 (d, J = 8.2 Hz, 1H), 7.28–7.19 (m, 2H), 7.12–7.10 (m, 6H), 6.99–6.96 (m, 4H), 6.65 (s, 1H), 5.46 (s, 1H), 2.26 (s, 3H), 1.97 (s, 3H), 1.58 (s, 3H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 168.3, 154.0, 152.5, 145.9, 143.8, 142.7, 137.0, 136.4, 133.3, 132.4, 130.0, 129.7, 129.5, 129.1, 128.8, 128.4, 128.2, 127.9, 126.3, 126.2, 125.0, 119.6, 118.0, 110.3, 52.5, 21.2, 17.9, 16.3. IR (KBr, cm⁻¹): 3406 (m), 2916 (w), 2165 (w), 1976 (w), 1637 (m), 1567 (m), 1505 (m), 1465 (s), 1365 (s), 1327 (m), 1298 (m), 1238 (s), 1201 (m), 1138 (m), 1100 (m), 1030 (m), 843 (s), 790 (m), 747 (s), 699 (s). Mp: 92–93 °C. Anal. Calcd. For C₃₂H₂₈N₂O: C, 84.18; H, 6.18; N, 6.14. Found: C, 84.12; H, 6.15; N, 6.19.

2-(1-(2,6-dibenzhydryl-4-methylphenylimino)ethyl)quinolin-8-ol (L5)

Using the above procedure, but 2,6-dibenzhydryl-4-methyl-benzenamine was used instead of 2-benzhydryl-4,6-dimethyl-benzenamine, the 2-(1-(2,6-dibenzhydryl-4-methylphenylimino)ethyl)quinolin-8-ol (L5) was obtained as a yellow green solid in 47.7% yield (0.58 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.23–8.16 (m, 2H), 8.00 (s, 1H), 7.50 (t, J = 7.9 Hz, 1H), 7.38 (d, J = 8.1 Hz, 1H), 7.29–7.15 (m, 13H), 7.03 (d, J = 6.8 Hz, 4H), 7.00 (d, J = 6.8 Hz, 4H), 6.70 (s, 2H), 5.28 (s, 2H), 2.19 (s, 3H), 1.05 (s, 3H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 169.6, 153.9, 152.6, 146.1, 143.9, 142.9, 142.6, 137.0, 136.3, 132.2, 132.0, 130.0, 129.7, 129.6, 129.0, 128.8, 128.6, 128.5, 128.2, 126.7, 126.4, 126.2, 119.7, 117.9, 110.2, 52.5, 21.5, 16.8. IR (KBr, cm⁻¹): 3405 (w), 3025 (w), 2167 (w), 1638 (m), 1599 (m), 1494 (s), 1445 (s), 1371 (w), 1334 (m), 1242 (s), 1077 (s), 1030 (m), 848 (m), 753 (s), 697 (s). Mp: 98–99 °C. Anal. Calcd. For C₄₄H₃₆N₂O: C, 84.18; H, 6.18; N, 6.14. Found: C, 84.12; H, 6.15; N, 6.19.

2-(1-(2,6-dibenzhydryl-4-isopropylphenylimino)ethyl)quinolin-8-ol (L6)

Using the above procedure, but 2,6-dibenzhydryl-4-isopropyl-benzenamine was used instead of 2,6-dibenzhydryl-4-methylbenzenamine, the 2-(1-(2,6-dibenzhydryl-4-isopropyl-phenylimino)ethyl)quinolin-8-ol (L6) was obtained as a yellow green solid in 29.1% yield (0.37 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.23–8.16 (m, 2H), 8.01 (s, 1H), 7.50 (t, J = 7.9 Hz, 1H), 7.38 (d, J = 8.1 Hz, 1H), 7.25–7.15 (m, 13H), 7.03 (d, J = 6.8 Hz, 4H), 6.99 (d, J = 6.8 Hz, 4H), 6.75 (s, 2H), 5.28 (s, 2H), 2.76–2.69 (m, 1H), 1.09 (s, 3H), 1.06 (d, J = 3.28 HZ, 6H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 169.5, 153.9, 152.6, 146.3, 143.9, 143.0, 142.7, 137.0, 136.3, 131.9, 130.0, 129.6, 129.0, 128.8, 128.4, 128.1, 126.3, 126.2, 126.1, 119.8, 117.9, 110.2, 52.5, 33.6, 24.2, 16.8. IR (KBr, cm⁻¹): 3407 (w), 2959 (w), 1632 (m), 1605 (m), 1564 (m), 1508 (m), 1493 (s), 1445 (s), 1371 (m), 1327 (m), 1287 (m), 1235 (s), 1199 (m), 1077 (m), 1030 (m), 841 (m), 738 (s), 696 (s). Mp: 104–105 °C. Anal. Calcd. For C₄₆H₄₀N₂O: C, 86.76; H, 6.33; N, 4.40. Found: C, 86.74; H, 6.35; N, 6.37.

Synthesis of nickel complexes (η⁵-cyclopentadienyl)titanium dichloride 2-((2-benzhydryl-4,6-dimethylphenylimino)methyl)quinolin-8-olate (C1)

To a 30 mL toluene solution of 0.442 g (1.00 mmol) 2-((2-benzhydryl-4,6-dimethylphenylimino)methyl)quinolin-8-ol, 0.040 g (1.00 mmol) KH was added at −78 °C. The mixture was stirred for additional 4 h, and then 0.219 g (1.00 mmol) CpTiCl₃ was added at −78 °C. The resultant mixture was slowly warmed up to room temperature and stirred for additional 6 h. After the solvent evaporation, the residue was extracted with CH₂Cl₂ (3 × 20 mL), and the filtrate was combined and concentrated to about 20 mL. The concentrated solution was covered with n-heptane and kept for three days to obtain brown crystals of (η⁵-cyclopentadienyl)titanium dichloride 2-((2-benzhydryl-4,6-dimethylphenylimino)methyl)quinolin-8-olate (C1) in 58.1% yield (0.37 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.32 (d, J = 8.4 Hz, 1H), 7.77 (t, J = 8.0 Hz, 1H), 7.44 (d, J = 8.1 Hz, 1H), 7.35 (t, J = 7.4 Hz, 1H), 7.28–7.22 (m, 5H), 7.17–7.11 (m, 4H), 7.08 (s, 2H), 6.99–6.93 (m, 1H), 6.96 (s, Cp, 5H), 6.78 (s, 1H), 6.56 (s, 1H), 2.39 (s, 3H), 2.31 (s, 3H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 168.6, 167.4, 149.2, 144.6, 143.2, 141.0, 139.2, 137.5, 136.7, 135.9, 133.3, 130.9, 130.7, 130.6, 130.0, 129.2, 128.9, 128.6, 128.4, 126.6, 126.5, 125.4, 125.1, 122.3, 121.5, 116.7, 111.8, 49.9, 21.3, 20.5. Anal. Calcd. For C₃₆H₃₀N₂Cl₂OTi: C, 69.14; H, 4.83; N, 4.48. Found: C, 69.11; H, 4.87; N, 4.47.

(η⁵-Cyclopentadienyl)titanium dichloride 2-(1-(2,6-dibenz-hydryl-4-methylphenylimino)methyl)quinolin-8-olate (C2)

Using the same procedure for C1, C2 was prepared by using L2 instead of L1 as brown crystals in 0.49 g (62.1%). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.27 (d, J = 8.1 Hz, 1H), 8.02 (d, J = 8.3 Hz, 1H), 7.48 (t, J = 7.6 Hz, 1H), 7.33 (d, J = 7.9 Hz, 1H), 7.25–7.11 (m, 14H), 7.02 (d, J = 6.0 Hz, 8H), 6.97 (s, Cp, 5H), 6.68 (s, 2H), 5.49 (s, 2H), 2.11 (s, 3H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 168.5, 165.7, 150.7, 147.4, 143.2, 142.5, 136.9, 133.1, 132.4, 129.8, 129.4, 129.8, 129.1, 128.9, 128.1, 128.2, 126.3, 125.9, 118.1, 117.9, 110.4, 53.5, 21.1. Anal. Calcd. For C₄₈H₃₈N₂Cl₂OTi: C, 74.14; H, 4.93; N, 3.60. Found: C, 74.16; H, 4.95; N, 3.65.

(η⁵-Cyclopentadienyl)titanium dichloride 2-(1-(2,6-dibenz-hydryl-4-isopropylphenylimino)methyl)quinolin-8-olate (C3)

Using the same procedure for C1, C3 was prepared by using L3 instead of L1 as brown crystals in 56.3% yield (0.46 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.41 (d, J = 8.3 Hz, 1H), 7.89 (t, J = 7.9 Hz, 1H), 7.66 (d, J = 8.3 Hz, 1H), 7.28–7.22 (m, 11H), 7.22–7.16 (m, 4H), 7.12–7.08 (t, J = 7.9 Hz, 4H), 7.01 (s, Cp, 5H), 6.81–6.76 (m, 4H), 6.04 (s, 1H), 2.76–2.71 (m, 1H), 1.07 (d, J = 6.8 Hz, 6H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 170.7, 162.8, 148.6, 146.7, 144.9, 144.0, 143.1, 140.8, 137.5, 130.7, 130.2, 129.8, 129.2, 128.5, 128.3, 127.6, 126.7, 126.5, 112.0, 50.5, 33.7, 23.9. Anal. Calcd. For C₅₀H₄₂N₂Cl₂OTi: C, 74.54; H, 5.25; N, 3.48. Found: C, 74.57; H, 5.21; N, 3.46.

(η⁵-Cyclopentadienyl)titanium dichloride 2-((2-benzhydryl-4,6-dimethylphenylimino)ethyl)quinolin-8-olate (C4)

Using the same procedure for C1, C4 was prepared by using L4 instead of L1 as brown crystals in 80.1% yield (0.51 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.45 (d, J = 8.6 Hz, 1H), 7.79 (t, J = 8.0 Hz, 1H), 7.49 (d, J = 8.5 Hz, 1H), 7.39–7.33 (m, 3H), 7.25–7.21 (m, 2H), 7.18–7.11 (m, 6H), 7.03 (d, J = 7.4 Hz, 2H), 6.96 (s, 1H), 6.81 (s, Cp, 5H), 6.66 (s, 1H), 2.32 (s, 3H), 2.28 (s, 3H), 1.12 (s, 3H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 171.3, 153.1, 152.8, 145.2, 143.6, 142.4, 137.5, 136.9, 133.1, 132.8, 130.4, 129.5, 129.3, 129.1, 128.8, 128.7, 128.2, 127.4, 126.6, 126.1, 125.4, 119.8, 118.1, 110.6, 54.1, 21.9, 17.2, 16.1. Anal. Calcd. For C₃₇H₃₂N₂Cl₂OTi: C, 69.50; H, 5.04; N, 4.38. Found: C, 69.54; H, 5.07; N, 4.34.

(η⁵-Cyclopentadienyl)titanium dichloride 2-(1-(2,6-dibenz-hydryl-4-methylphenylimino)ethyl)quinolin-8-olate (C5)

Using the same procedure for C1, C5 was prepared by using L5 instead of L1 as brown crystals in 41.8% yield (0.33 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.27–8.11 (m, 2H), 7.53 (t, J = 7.9 Hz, 1H), 7.32 (d, J = 8.1 Hz, 1H), 7.29–7.15 (m, 13H), 7.02 (d, J = 6.8 Hz, 4H), 7.00 (d, J = 6.8 Hz, 4H), 6.74 (s, Cp, 5H), 6.71 (s, 2H), 5.23 (s, 2H), 2.17 (s, 3H), 1.04 (s, 3H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 170.6, 154.3, 152.1, 145.7, 144.1, 142.3, 142.9, 138.1, 135.3, 132.8, 132.1, 130.3, 129.4, 129.6, 129.1, 128.8, 128.6, 128.5, 128.1, 126.9, 126.2, 125.9, 119.9, 118.1, 110.4, 53.1, 21.8, 16.3. Anal. Calcd. For C₄₉H₄₀N₂Cl₂OTi: C, 74.34; H, 5.09; N, 3.54. Found: C, 74.36; H, 5.05; N, 3.51.

(η⁵-Cyclopentadienyl)titanium dichloride 2-(1-(2,6-dibenz-hydryl-4-isopropylphenylimino)ethyl)quinolin-8-olate (C6)

Using the same procedure for C1, C6 was prepared by using L6 instead of L1 as brown crystals in 55.1% yield (0.45 g). ¹H NMR (CDCl₃, 400 MHz, ppm): δ 8.33 (d, J = 11.3 Hz, 1H), 7.76 (t, J = 11.3 Hz, 1H), 7.44 (d, J = 10.9 Hz, 1H), 7.38–7.29 (m, 6H), 7.21–7.14 (m, 6H), 7.10–7.08 (m, 7H), 6.99–6.94 (m, 3H), 6.91 (s, 5H, Cp), 6.84 (s, 2H), 6.68 (s, 1H), 5.85 (s, 1H), 2.84–2.66 (m, 1H), 1.25 (s, 3H), 1.19 (d, J = 9.16 Hz, 3H), 1.05 (d, J = 9.08 Hz, 3H). ¹³C NMR (CDCl₃, 100 MHz, ppm): δ 171.5, 153.3, 152.6, 146.3, 143.9, 143.1, 142.7, 137.0, 136.3, 131.7, 130.2, 129.4, 129.6, 128.4, 128.2, 128.1, 126.7, 126.2, 126.1, 119.4, 118.0, 110.4, 52.1, 33.1, 24.8, 16.1. Anal. Calcd. For C₅₁H₄₄N₂Cl₂OTi: C, 74.73; H, 5.41; N, 3.42. Found: C, 74.77; H, 5.46; N, 3.45.

X-ray crystallographic study

Crystals of C2 and C4 suitable for single-crystal X-ray analysis were obtained by laying n-heptane on the dichloromethane solutions. Single-crystal X-ray diffraction for C2 and C4 was performed on a Rigaku RAXIS Rapid IP diffractometer with graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) at 173(2) K. Cell parameters were obtained by global refinement of the positions of all collected reflections. Intensities were corrected for Lorentz and polarization effects and empirical absorption. The structures were solved by direct methods and refined by full-matrix least-squares on F². All non-hydrogen atoms were refined anisotropically. Structure solution and refinement were performed by using the SHELXL-97 package.⁶⁴ Crystal data collection and refinement details are given in Table 6.

Table 6 Crystallographic data and refinement details for complexes C2 and C4

	C2	C4
Empirical formula	C48H38Cl2N2OTi	C37H32Cl2N2OTi
Formula weight	777.60	639.45
Crystal color	Red	Red
T/K	173(2)	173(2)
Wavelength (Å)	0.71073	0.71073
Crystal system	Orthorhombic	Monoclinic
Space group	Pbca	C2/c
a/Å	17.529(4)	53.675(11)
b/Å	18.752(4)	10.021(2)
c/Å	25.656(5)	24.886(5)
α/°	90	90
β/°	90	100.29(3)
γ/°	90	90
Volume/Å^3	8433(3)	13170(5)
Z	8	16
Dcalc/Mg m^−3	1.225	1.290
μ/mm^−1	0.366	0.454
F(000)	3232	5312
Crystal size/mm	0.35 × 0.20 × 0.05	0.32 × 0.20 × 0.18
θ range/°	1.59–25.34	0.77−25.00
Limiting indices	−18 ≤ h ≤ 20,	−63 ≤ h ≤ 63,
	−22 ≤ k ≤ 12,	−11 ≤ k ≤ 11,
	−30 ≤ l ≤ 20	−29 ≤ l ≤ 19
No. of rflns collected	24720	25332
No. of unique rflns	7661	11535
R int	0.0828	0.0639
Completeness to θ/%	99.3 (θ = 25.34)	99.5(θ = 25.00)
Goodness-of-fit on F^2	1.153	1.069
Final R indices [I > 2σ(I)]	R1 = 0.1065,	R1 = 0.0932,
	wR2 = 0.2577	wR2 = 0.2446
R indices (all data)	R1 = 0.1428,	R1 = 0.1193,
	wR2 = 0.2817	wR2 = 0.2632

---

Procedures for ethylene homo- and co-polymerization

A stainless steel autoclave (0.5 L) equipped with a mechanical stirrer and a temperature controller was heated in vacuum at 80 °C and recharged with ethylene three times, then cooled to room temperature under ethylene atmosphere. A toluene solution of the titanium pre-catalyst (with co-monomer) was transferred into the reactor. After the desired reaction temperature was reached and the required amount of co-catalyst (with 100 mL volume in total) was added, the autoclave was immediately pressurized to 10 atm. The ethylene pressure was kept constant during the reaction through the feeding of ethylene. After the required time, the feeding of ethylene was stopped, and the autoclave was placed in a water-ice bath for one hour. The resultant mixture was poured into acidic ethanol containing 10% hydrochloric acid, and the solid polymer was collected and washed with water and ethanol several times and dried under vacuum to constant weight.

Acknowledgements

This work is supported by NSFC No. 20904059 as well as the MOST 863 program No. 2009AA034601. The EPSRC are thanked for the awarded of a travel grant (to CR).

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Footnote

† CCDC reference numbers 869824 and 869825 for crystallographic data of complexes C2 and C4. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c2cy20240a

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