2-(1-Aryliminopropylidene)quinolylcobalt(II) dichlorides: synthesis, characterization and catalytic behaviour towards ethylene

Abstract

A series of 2-(1-aryliminopropylidene)quinolines and their cobalt(II) chlorides were synthesized and characterized. Activation with methylaluminoxane (MAO) under 10 atm ethylene pressure, all the cobalt procatalysts exhibited good activities for ethylene dimerization at room temperature, however, performed ethylene polymerization at elevated reaction temperatures. Sole ethylene polymerization was achieved at 10 atm ethylene at 90 °C. The polyethylenes obtained indicated that the molecular weight ranged from 92.5 Kg mol⁻¹ to 176.9 Kg mol⁻¹ with narrower molecular weight distributions (2.82–4.17).

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1. Introduction

The discovery of bis(imino)pyridylmetal (Fe or Co) chlorides (A, Scheme 1)¹ symbolized a milestone of late-transition metal procatalysts in ethylene polymerization and oligomerization.² Subsequently, bis(imino)pyridylmetal (Fe or Co) procatalysts have been extensively investigated through changing substituents of bis(imino)pyridines,³ for understanding the active species and the mechanisms.⁴ Meanwhile, tremendous efforts have been spent on designing N-heterocyclic compounds as ligands, and the catalytic behaviour of their metal (Fe or Co) complexes were explored in ethylene reactivity.⁵ In the past decade, metal (Fe or Co) complexes bearing tridentate ligands have been focused on ethylene oligomerization and polymerization in our group,^2g,h and those interesting ligands (Scheme 1) included 2-benzimidazolyl-6-iminopyridines (B),⁶ 2-quinoxalinyl-6-iminopyridines (C),⁷ 2-imino-1,10-phenanthrolines (D),⁸ 2-(benzimidazol-2-yl)-1,10-phenanthrolines (E),⁹iminoquinolyl derivatives (F),¹⁰ 2-methyl-2,4-bis-(6-iminopyridin-2-yl)-1H-1,5-benzodiazepines (G),¹¹ 2-benzoxazolyl-6-imino-pyridines (H),¹² and 2,8-bis(imino)quinolylmetal (Fe or Co) procatalysts (I).¹³ In general, the late-transition metal procatalysts deactivated and produced more oligomers when the reaction temperature was elevated. However, there were two exceptional cobalt models of H^12a and I,¹³ which favourably performed ethylene polymerization at elevated reaction temperatures. Considering the distorted square-based pyramidal geometry of 2,8-bis[1-(2,6-dimethylphenylimino) ethyl]quinolylcobalt dichloride,¹³ the bidentate ligands of iminoquinolines are promising. According to previous reports, cobalt complexes bearing bidentate ligands (J, Scheme 1) showed interesting results in ethylene reactivity.¹⁴ Therefore, the 2-iminoquinolines are purposely synthesized and used in preparing the title complexes (K, Scheme 1). After activation with methylaluminoxane (MAO), all the cobalt procatalysts exhibited high activity for ethylene dimerization at ambient temperature, but ethylene polymerization was achieved at elevated reaction temperatures. Besides tridentate cobalt procatalysts,^12a this is the first example for cobalt complexes with bidentate ligands performing the temperature-switching ethylene reactivity and favouring polymerization at elevated temperatures. Herein, the synthesis and characterization of the title complexes and their catalytic behaviour are reported and discussed.

Scheme 1 Model procatalysts.

2. Results and discussion

2.1 Synthesis and characterization

The stoichiometric condensation reaction of 2-propionyl quinoline with corresponding anilines with a catalytic amount of p-toluenesulfonic acid in toluene gave 2-(1-arylimino propylidene)quinoline derivatives (L1–L6) in good isolated yields, and further reaction with anhydrous CoCl₂ in ethanol formed the cobalt complexes in high yields (Scheme 2).

Scheme 2 Synthetic procedures.

All organic compounds were routinely characterized by elemental analysis, ¹H and ¹³C NMR and IR spectra, and their cobalt complexes were characterized by elemental analysis, FT-IR and MALDI-TOF mass measurement. According to their IR spectra, the stretching vibrations of C–N in these complexes (1603–1621 cm⁻¹) apparently shift to lower wavenumbers with greatly reduced intensities compared to those of the corresponding ligands (1641–1647 cm⁻¹), indicating the effective coordination interaction between the imino-nitrogen and the cobalt. According to the mass spectra, monomeric cobalt cationic species with losing one chlorine were observed in all cases, indicating the monomeric feature in the solution. The unambiguous molecular structures of C2 and C3 were further confirmed by X-ray diffraction analysis, indicating the monomeric for C3 and the aggregating dimeric for C2 in the solid state. Metal complex halides were sometime present monomeric molecules in solution but dimeric in the solid states through halo-bridges.^14a,15

2.2 Crystal structures

Single crystals of complexes C2 suitable for X-ray diffraction analysis were grown by slow layer diffusion of diethyl ether into its DMF solution. However, single crystals of C3 were obtained by diffusing a diethyl ether layer into its solution in methanol. Their structures are depicted in Fig. 1 and 2, respectively, with selected bond lengths and angles.

Fig. 1 Molecular structure of C2. Thermal ellipsoids are shown at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): Co1–N1, 2.154(2); Co1–N2, 2.061(3); Co1–Cl1, 2.2753(10); Co1–Cl2, 2.4376(9); N2–C10, 1.446(4); N2–C16, 1.286(4); N1–C1, 1.330(4); N1–C9, 1.360(4); N2–Co1–N1, 76.95(10); N2–Co1–Cl1, 116.88(8); N2–Co1–Cl2, 97.60(8); N1–Co1–Cl1, 91.88(7); N1–Co1–Cl2, 172.92(7); Cl2–Co1–Cl1, 94.64(4).

Fig. 2 Molecular structure of C3. Thermal ellipsoids are shown at the 30% probability level. Hydrogen atoms have been omitted for clarity. Selected bond lengths (Å) and angles (°): Co1–N1, 2.047(2); Co1–N2, 2.035(2); Co1–Cl1, 2.2202(10); Co1–Cl2, 2.2087(9); N2–C10, 1.449(3); N2–C16, 1.288(3); N1–C1, 1.332(3); N1–C9, 1.367(3); N2–Co1–N1, 80.62(9); N2–Co1–Cl1, 113.91(7); N2–Co1–Cl2, 117.03(7); N1–Co1–Cl1, 106.90(7); N1–Co1–Cl2, 117.26(7); Cl2–Co1–Cl1, 115.88(4).

In C2, a centrosymmetric dicobalt center is shown with two chloro-bridges. Each cobalt atom is coordinated by two nitrogen atoms of the ligand, one terminal chlorine atom (Cl1), and two bridged chlorine atoms (Cl2 and Cl2A). The five-coordinate cobalt center forms a distorted trigonal bipyramid coordination. The Co1–N1 bond length is 2.154(2) Å, longer than that of Co1–N2 bond. The distance between the cobalt and the terminal chlorine (Co1–Cl1) is 2.2753(10) Å, whereas, the bond lengths between the cobalt and another two bridging chlorines are different significantly (Co1–Cl2 = 2.4376(9) and Co1–Cl2A = 2.3451(10) Å). The Co⋯Co length is 3.460 Å, indicating no direct metal–metal interaction. The Co1 atom deviates by 0.095 Å from the plane of the Cl2–N1–Cl2 atoms. The dihedral angle between the plane of Cl1–Co1–Cl2 and the plane of N1–Co1–N2 is 62.77°, significantly different from that of complex C3. The dihedral angle between the quinolinyl plane and the plane of the phenyl ring is 85.31°.

The four-coordinate complex C3 (Fig. 2) shows a distorted tetrahedral geometry around the cobalt. Two Co–N bonds have nearly similar bond lengths. The Co1–Cl1 bond length [2.2202(10) Å] are longer than the bond lengths of Co1–Cl2 [2.2087(9) Å], and both of the Co–Cl bond length are shorter than those of complex C2. The dihedral angle formed by Cl1–Co1–Cl2 and N1–Co1–N2 is 86.54°. In the five-membered cobaltacycle N2–C16–C1–N1–Co1, all atoms almost lie in the same plane with the largest deviation of 0.136 Å for N1 and 0.046 Å for Co, while the sum of internal ring angles (539°) is close to the idea value of 540°. The plane formed by the quinolinyl and the plane of phenyl ring on imino group are nearly vertical with the dihedral angle of 83.34°.

2.3 Ethylene dimerization and polymerization

2.3.1 Ethylene dimerization . During the selection of a suitable co-catalyst, methylaluminoxane (MAO), modified methylaluminoxane (MMAO), and diethylaluminium chloride (Et₂AlCl) were used and positive responses were found in the presence of MAO and MMAO. However, the low activities were observed at an ambient pressure of ethylene. Therefore a pressure of 10 atm of ethylene was used along with the molar ratio of Al/Co in 1000 at room temperature, the dimerization activity reached 1.9 × 10⁶ g mol⁻¹ (Co) h⁻¹ using MAO, and 9.4 × 10⁵ g mol⁻¹ (Co) h⁻¹ using MMAO. Subsequently, the MAO was selected for further investigation, and the catalytic system of C3/MAO at 10 atm ethylene was typically investigated with varying reaction parameters (Table 1).

Table 1 Catalytic performance of C3/MAO

Entry	Al/Co	T/°C	Butene			Polymer
			Product yield/g^a	Activity^b	α-C4/∑C4 (%)^a	Product yield/mg	Activity^c
Condition: 5 μmol Complex, 30 min, 100 mL toluene.a Determined by GC.b 10^5 g mol^−1 (Co) h^−1.c 10^4 g mol^−1 (Co) h^−1.
1	500	20	0.48	1.9	32.2	—	—
2	750	20	1.08	4.3	40.1	—	—
3	1000	20	4.75	19	59.8	—	—
4	1250	20	1.93	7.7	47.9	—	—
5	1500	20	1.58	6.3	46.4	—	—
6	1000	40	1.45	5.8	44.3	—	—
7	1000	60	1.18	4.7	40.8	—	—
8	1000	80	1.08	4.3	41.2	15	0.63
9	1000	90	—	—	—	23	0.91

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As shown in Table 1, the optimum condition for ethylene dimerization was using the Al/Co molar ratio of 1000 at room temperature. Changing the Al/Co molar ratio or elevating the reaction temperature caused the catalytic activity to gradually decrease. Such phenomena have been commonly observed in catalytic systems of late-transition metal procatalysts. Interestingly, both butenes and polyethylene were observed with low activity at 80 °C. Surprisingly, further increasing temperature up to 90 °C, polyethylenes were only obtained without noticing any oligomers. Therefore the detail study was carried out in both ethylene dimerization and polymerization. The ethylene dimerization by all procatalysts with the Al/Co molar ratio of 1000 at 20 °C and 10 atm was preceded, and their results were tabulated in Table 2.

Table 2 Ethylene dimerization at 20 °C with the Al/Co molar ratio of 1000

Entry	Complex	Butene yield/g^a	Activity^b	α-C4/∑C4^a
Condition: 5 μmol Complex, 30 min, 100 mL toluene.a Determined by GC.b 10^5 g mol^−1 (Co) h^−1.
1	C1	2.11	8.4	53.3%
2	C2	2.51	10	57.6%
3	C3	4.75	19	59.8%
4	C4	2.43	9.7	51.8%
5	C5	3.02	12	59.8%
6	C6	1.91	7.6	56.4%

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According to Table 2 (entries 1–5), similar to cobalt procatalysts in the literature,^14b–f current procatalysts showed high activity in ethylene dimerization. The catalytic activities were in the order C3 > C2 > C1 and C5 > C4, and all higher than C6. The more bulky substituents of ligands protected the active sites, therefore active species was maintained.^3c The tendency of catalytic activities with substituent influences was not consistent with the calculation simulation for N⁁N⁁N-tridentate late-transition metal procatalysts,^14e,16 which indicated the higher net charge of the metal centre performed better catalytic activity. In the current system, the bidentate ligands provided less electronic donations to the metal center. Regarding observations by C2vs.C5 and C1vs.C4, the procatalysts bearing ligands with an additional methyl group showed better activity because of a better solubility in solution, consistent with the literature.¹

2.3.2 Ethylene polymerization . When operated at 90 °C with 10 atm ethylene for 30 min, the trials of C3/MAO was investigated with finding the optimum molar ratio as 3000 (entries 1–6, Table 3). By increasing the reaction temperature up to 100 °C, the activity was slightly decreased (entries 4 vs. 7, Table 3) due to lower ethylene solubility at higher temperatures.¹⁷ As a consequence, other cobalt procatalysts were studied with the molar ratio of Al/Co 3000 at 90 °C and 10 atm for 30 min (entries 8–12, Table 3). Their catalytic activities were in the order C3 > C2 > C1 > C6 and C5 > C4 > C6, which is consistent with the activity tendency for ethylene dimerization at room temperature.

Table 3 Ethylene polymerization with MAO at 10 atm within 30 min

Entry	Complex	Al/Co	T/°C	Product yield/mg	Activity^a	T m/°C^b	M w ^c × 10^−4	M w/Mn^c
Condition: 5 μmol Co, 100 mL toluene.a 10^4 g mol^−1 (Co) h^−1.b Determined by DSC.c Determined by GPCvs.polystyrene standards.
1	C3	1000	90	23	0.91	131.6	—	—
2	C3	2000	90	35	1.4	132.7	10.27	3.40
3	C3	2500	90	58	2.3	133.2	11.69	3.57
4	C3	3000	90	130	5.2	133.4	12.54	3.79
5	C3	3500	90	108	4.3	133.7	13.51	3.99
6	C3	4000	90	103	4.1	133.0	11.32	4.17
7	C3	3000	100	98	4.0	133.1	12.97	4.14
8	C1	3000	90	105	4.2	133.0	11.16	3.87
9	C2	3000	90	115	4.6	132.8	9.54	3.98
10	C4	3000	90	113	4.5	132.9	10.73	3.97
11	C5	3000	90	123	4.9	132.4	9.25	2.82
12	C6	3000	90	98	4.0	132.7	10.41	3.72

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According to their GPC data, the polyethylenes obtained had similar molecular weights and narrow molecular weight distributions (2.82–4.17), and the similar active species were assumed for those cobalt procatalysts. The higher temperature (entry 7, Table 3) and more MAO (entries 5 and 6, Table 3) used, resulted in polyethylenes with broader molecular weight distributions because of multi-active species that formed.^13,18 Considering molecular weights of polyethylenes formed and the activity data, even imaging an active species producing one polymeric chain, there were less than 10% of cobalt complexes transferred into active species for such polymerization. In the dimerization process at ambient temperature, the activities were obtained one-order higher. Therefore, there are more active species formed at low reaction temperature, indicating that either less active species are formed or the ligands can not sufficiently protect the active species at elevated temperatures.^5a Though bidentate cobalt complexes bearing iminopyridine ligands^14a and α-diimine ligands^14g,h were investigated, the current cobalt procatalysts showed the highest activity in ethylene polymerization, especially at 90 °C.

In general, ethylene oligomerization and polymerization are considered as the competitive reactions of chain propagation and chain transfer. In the current catalytic systems two different active species formed at different reaction temperatures. Though most bidentate cobalt complexes show lower activity in ethylene polymerization,^14a,g,h newly active species were potentially formed in the current cobalt system when the catalytic system was heated up to above 80 °C in the presence of MAO. The bidentate cobalt complexes were stable in toluene for three hours at 100 °C without noticing any change; however, the colour of the cobalt solution changed with adding 1000 equiv. of MAO. Considering a higher amount of butenes (in terms of weight) formed at a lower temperature than the amount of polyethylenes at a high temperature, suggests the active species was easily formed at the lower reaction temperature with possibly repeating dimerization. However, one of several cobalt complex molecules would be transferred as an active species acting for ethylene polymerization, which could be one cobalt species (with most cobalt deactivated) or several cobalt complexes aggregating together as an multi-nuclear species. Therefore, two kinds of characteristic active species were assumed at different reaction temperatures.

3. Conclusion

The 2-(1-aryliminopropylidene)quinolylcobalt(II) dichlorides, when activated with MAO, showed high activities in ethylene dimerization at ambient temperature, and considerable activities in ethylene polymerization at 90 °C. Two kinds of active species are potentially formed and performed in ethylene reactivity at different temperatures. It is assumed that only partially active species could be formed at higher temperatures. In the current cobalt procatalysts, the more bulky substituents of the ligands that were used, the better the activities observed. The bidentate cobalt complexes in ethylene reactivity would stimulate a more extensive study.

4. Experimental

4.1 General considerations

All manipulations of air- and moisture-sensitive compounds were performed under a nitrogen atmosphere using standard Schlenk techniques. Toluene was refluxed over sodium benzophenone and distilled under argon prior to use. Methylaluminoxane (MAO, a 1.46 M solution in toluene) and modified methylaluminoxane (MMAO, 1.93 M in heptane, 3A) were purchased from Akzo Nobel Corporation. Other reagents were purchased from Aldrich or Acros Chemicals. ¹H and ¹³C NMR spectra were recorded on a Bruker DMX 300 MHz or a Bruker DMX 400 MHz instrument at ambient temperature using TMS as an internal standard. IR spectra were recorded on a Perkin-Elmer System 2000 FT-IR spectrometer. Elemental analysis was carried out using an HPMOD 1106 microanalyzer. MALDI-TOF mass spectra were obtained with a Bruker Autoflex III matrix-assisted laser desorption/ionization time of-flight mass spectrometer, with DHB as the matrix. GC analysis was performed with a VARIAN CP-3800 gas chromatograph equipped with a flame ionization detector and a 30 m (0.2 mm i.d., 0.25 μm film thickness) CP-Sil 5 CB column. The yield of oligomers was calculated by referencing with the mass of the solvent on the basis of the prerequisite that the mass of each fraction was approximately proportional to its integrated areas in the GC trace. Selectivity for the linear α-olefin was defined as (amount of linear α-olefin of all fractions)/(total amount of oligomer products) in percent. The molecular weights and the polydispersities of the polymer samples were determined at 150 °C by a PL-GPC 220 type high-temperature chromatograph equipped with three PLgel 10 mm Mixed-B LS type columns. 1,2,4-Trichlorobenzene (TCB) was employed as the solvent at a flow rate of 1.0 mL min⁻¹. The calibration was made by using a polystyrene standard.

4.2 Syntheses

2-Propionylquinoline . Provided by Astatech, Inc. (www.astatechinc.com). M.p.: 79–81 °C. IR (KBr, cm⁻¹): 3001 (w), 1695 (s), 1668 (s), 1593 (s), 1557 (s), 1428 (m), 1361 (m), 1279 (s), 1259 (s), 1207 (s), 1095 (s), 856 (s), 775 (s), 615 (s). ¹H NMR (300 MHz, CDCl₃): δ 8.28 (d, J = 11.4 Hz, 1 H, quin), 8.20 (d, J = 11.3 Hz, 1 H, quin), 8.14 (d, J = 11.4 Hz, 1 H, quin), 7.88 (d, J = 10.8 Hz, 1 H, quin), 7.81 (t, J = 9.5 Hz, 1 H, quin), 7.66 (t, J = 10.1 Hz, 1 H, quin), 3.43 (q, J = 7.3 Hz, 2 H, CH₂CH₃), 1.30 (t, J = 7.3 Hz, 3 H, CH₂CH₃). ¹³C NMR (75 MHz, CDCl₃): 203.1, 153.1, 147.3, 136.9, 130.6, 130.0, 128.5, 127.7, 118.2, 30.9, 8.2. Anal. calcd for C₁₂H₁₁NO: C 77.81, H 5.99, N 7.56. Found: C 77.52, H 5.78, N 7.55.

2-(1-(2,6-Dimethylphenylimino)propylidene)quinoline L1. A mixture of 2,6-dimethylaniline (0.9213 g, 6 mmol), 2-propionylquinoline (0.93 g, 5 mmol), and a catalytic amount of p-toluenesulfonic acid in toluene (60 mL) was refluxed for 24 h. After solvent evaporation, the crude product was purified by column chromatography on silica gel with petroleum ether as eluent to afford the product as a yellow powder in 66%. M.p.: 114–116 °C. IR (KBr, cm⁻¹): 2940 (w), 1647 (s), 1593 (m), 1467 (s), 1441 (m), 1360 (m), 1205 (m), 1091 (m), 763 (s).¹H NMR (400 MHz, CDCl₃): δ 8.46 (d, J = 8.6 Hz, 1 H, quin), 8.24 (d, J = 8.6 Hz, 1 H, quin), 8.17 (d, J = 8.4 Hz, 1 H, quin), 7.87 (d, J = 8.1 Hz, 1 H, quin), 7.76 (t, J = 8.1 Hz, 1 H, quin), 7.60 (t, J = 7.1 Hz, 1 H, quin), 7.09 (d, J = 7.5 Hz, 2 H, aryl), 6.97 (t, J = 7.6 Hz, 1 H, aryl), 2.83 (q, J = 7.6 Hz, 2 H, CH₂CH₃), 2.09 (s, 6 H, Ar-CH₃), 1.07 (t, J = 7.6 Hz, 3 H, CH₂CH₃). ¹³C NMR (100 MHz, CDCl₃): 172.3, 155.6, 148.7, 147.6, 136.3, 130.3, 129.6 128.8, 128.0 127.7, 127.4, 125.4, 123.1, 119.7, 23.3, 18.3, 11.5. Anal. calcd for C₂₀H₂₀N₂: C 83.30, H 6.99, N 9.71. Found: C 83.42, H 6.83, N 9.69.

2-(1-(2,6-Diethylphenylimino)propylidene)quinoline L2. Using the same procedure as for the synthesis of L1, L2 was obtained as a yellow powder in 56% yield. M.p.: 115–117 °C. IR (KBr, cm⁻¹): 3056 (m), 2926 (m), 1636 (s), 1589 (m), 1566 (m), 1453 (s), 1362 (s), 1280 (m), 1257 (m), 1198 (m), 1187 (m), 1095 (s), 876 (m), 856 (m), 767 (s).¹H NMR (400 MHz, CDCl₃): δ 8.45 (d, J = 8.5 Hz, 1 H, quin), 8.18 (t, J = 8.5 Hz, 2 H, quin), 7.84 (d, J = 9.5 Hz, 1 H, quin), 7.73 (t, J = 7.4 Hz, 1 H, quin), 7.57 (t, J = 7.4 Hz, 1 H, quin), 7.14 (d, J = 7.3 Hz, 2 H, aryl),7.06 (t, J = 7.4 Hz, 1 H, aryl), 2.83 (q, J = 7.4 Hz, 2 H, CH₂CH₃), 2.51–2.45 (m, 2 H, Ar-CH₂CH₃), 2.40–2.32 (m, 2 H, Ar-CH₂CH₃), 1.21 (t, J = 7.4 Hz, 6 H, Ar-CH₂CH₃), 1.09 (t, J = 7.4 Hz, 3 H, CH₂CH₃). ¹³C NMR (100 MHz, CDCl₃): 171.7, 155.6, 147.7, 147.6, 136.2, 131.0, 130.3, 129.5, 128.7, 127.7, 127.4, 125.8, 123.3, 119.7, 24.7, 23.5 26.2, 13.6, 11.5. Anal. calcd for C₂₂H₂₄N₂: C 83.50, H 7.64, N 8.85. Found: C 83.47, H 7.96, N 8.66.

2-(1-(2,6-Diisopropylphenylimino)propylidene)quinoline L3. Using the same procedure as for the synthesis of L1, L3 was obtained as a yellow powder in 69% yield. M.p.: 134–136 °C. IR (KBr, cm⁻¹): 3062 (w), 2962 (s), 1645 (s), 1591 (m), 1565 (m), 1461 (m), 1435 (m), 1363 (m), 1277 (m), 1185 (m), 1095 (m), 856 (m), 765(s). ¹H NMR (400 MHz, CDCl₃): δ 8.42 (d, J = 8.6 Hz, 1 H, quin), 8.24 (d, J = 8.6 Hz, 1 H, quin), 8.18(d, J = 8.4 Hz, 1 H, quin), 7.88 (d, J = 8.0 Hz, 1 H, quin), 7.76 (t, J = 7.4 Hz, 1 H, quin), 7.61 (t, J = 7.4 Hz, 1 H, quin), 7.18 (d, J = 7.5 Hz, 2 H, aryl), 7.12 (t, J = 7.3 Hz, 1 H, aryl), 2.87–2.76 (m, 4 H), 1.23 (d, J = 6.8 Hz, 6 H, Ar-CH(CH₃)₂), 1.15 (d, J = 6.8 Hz, 6 H, Ar-CH(CH₃)₂), 1.10 (t, J = 7.5 Hz, 3 H, CH₂CH₃). ¹³C NMR (100 MHz, CDCl₃): 171.4, 155.7, 147.6, 146.4, 136.2, 135.6, 130.2, 128.7, 127.7, 127.3, 123.6, 123.0, 119.8, 28.4, 23.7, 22.4, 11.3. Anal. calcd for C₂₄H₂₈N₂: C 83.68, H 8.19, N 8.13. Found: C 83.47, H 7.92, N 8.46.

2-(1-(2,4,6-Trimethylphenylimino)propylidene)quinoline L4. Using the same procedure as for the synthesis of L1, L4 was obtained as a yellow powder in 58% yield. M.p: 121–122 °C. IR (KBr, cm⁻¹): 2982 (w), 2913 (w), 1641 (s), 1568 (m), 1477 (s), 1361 (m), 1276 (m), 1215 (m), 1147 (m), 1097 (m), 858 (s), 771 (m).¹H NMR (400 MHz, CDCl₃): δ 8.45 (d, J = 8.6 Hz, 1 H, quin), 8.23 (d, J = 8.6 Hz, 1 H, quin), 8.17 (d, J = 8.4 Hz, 1 H, quin), 7.87 (d, J = 8.0 Hz, 1 H, quin), 7.76 (t, J = 7.4 Hz, 1 H, quin), 7.60 (t, J = 7.4 Hz, 1 H, quin), 6.90 (s, 2 H, aryl), 2.83 (q, J = 7.6 Hz, 2 H, CH₂CH₃), 2.30 (s, 3 H, Ar-CH₃), 2.05 (s, 6 H, Ar-CH₃), 1.06 (t, J = 7.6 Hz, 3 H, CH₂CH₃). ¹³C NMR (100 MHz, CDCl₃): 172.5, 155.7, 147.6, 146.4, 136.2, 135.6, 130.2, 128.7, 127.7, 127.3, 123.6, 123.0, 119.8, 28.4, 23.7, 22.4, 11.3. Anal. calcd for C₂₁H₂₂N₂: C 83.40, H 7.33, N 9.26. Found: C 83.44, H 7.52, N 8.99.

2-(1-(2,6-Diethyl-4-methylphenylimino)propylidene) quinoline L5. Using the same procedure as for the synthesis of L1, L5 was obtained as a yellow powder in 63% yield. M.p.: 115–117 °C. IR (KBr; cm⁻¹): 3056 (m), 2926 (m), 1636 (s), 1589 (m), 1566 (m), 1453 (s), 1362 (s), 1280 (m), 1257 (m), 1198 (m), 1187 (m), 1095 (s), 876 (m), 856 (m), 767 (s).¹H NMR (400 MHz, CDCl₃): δ 8.42 (d, J = 8.6 Hz, 1H, quin), 8.22 (d, J = 8.6 Hz, 1 H, quin), 8.16 (d, J = 8.4 Hz, 1 H, quin), 7.87 (d, J = 8.0 Hz, 1 H, quin), 7.74 (t, J = 7.5 Hz, 1 H, quin), 7.59 (t, J = 7.5 Hz, 1 H, quin), 7.06 (s, 2 H, aryl), 2.82 (q, J = 7.5 Hz, 2 H, CH₂CH₃), 2.51–2.45 (m, 2 H), 2.40–2.32 (m, 5 H), 1.17 (t, J = 7.5 Hz, 6 H, Ar-CH₂CH₃), 1.05 (t, J = 7.5 Hz, 3 H, CH₂CH₃). ¹³C NMR (100 MHz, CDCl₃): 171.9, 155.9, 147.5, 145.2, 136.2, 132.4, 130.9, 130.2, 129.5, 128.7, 127.7, 127.3, 126.6, 119.7, 24.7, 23.4 21.2, 13.7, 11.5. Anal. calcd for C₂₂H₂₄N₂: C 83.59, H 7.93, N 8.48. Found: C 83.47, H 7.96, N 8.66.

2-(1-(2,6-Dichlorophenylimino)propylidene)quinoline L6. The 1-(quinolin-2-yl)propan-1-one (1.442 g, 17.0 mmol), 2,6-dichloroaniline (1.4778 mg, 34.0 mmol), and p-toluenesulfonic acid (0.120 g) were combined with tetraethyl silicate (5 mL) in a flask. The flask was equipped with a condenser along with a water knockout trap, and the mixture was refluxed under nitrogen for 28 h. Tetraethyl silicate was removed at reduced pressure, and the resulting solid was eluted with petroleum ether on an alumina column. The first eluting part was collected and concentrated to give a yellow solid in 23% yield. M.p.: 120–122 °C. IR (KBr, cm⁻¹): 2940 (w), 1647 (s), 1593 (m), 1467 (s), 1441 (m), 1360 (m), 1205 (m), 1091 (m), 763 (s).¹H NMR (400 MHz, CDCl₃): δ 8.46 (d, J = 8.6 Hz, 1 H, quin), 8.26 (d, J = 8.6 Hz, 1 H, quin), 8.19 (d, J = 8.4 Hz, 1 H, quin), 7.88 (d, J = 8.1 Hz, 1 H, quin), 7.77 (t, J = 8.1 Hz, 1 H, quin), 7.62 (t, J = 7.5 Hz, 1 H, quin), 7.38 (d, J = 8.1 Hz, 2 H, aryl), 6.99 (t, J = 8.0 Hz, 1 H, aryl), 2.92 (q, J = 7.6 Hz, 2 H, CH₂CH₃), 1.16 (t, J = 7.6 Hz, 3 H, CH₂CH₃). ¹³C NMR (100 MHz, CDCl₃): 176.2, 154.8, 147.6, 145.6, 136.5, 130.4, 129.7 129.0, 128.3 127.7, 124.5, 124.3, 120.0, 24.7, 11.4. Anal. calcd for C₁₈H₁₄Cl₂N₂: C 65.67, H 4.29, N 8.51. Found: C 65.44, H 4.30, N 8.71.

2-(1-(2,6-Dimethylphenylimino)propylidene)quinolylcobalt dichloride C1. A typical synthetic procedure for C1 can be described as follows. To a mixture of 2-(1-(2,6-dimethylphenylimino) propylidene)quinoline (L1) (156 mg, 0.54 mmol) and CoCl₂ (71 mg, 0.54 mmol) was added ethanol (8 mL) at room temperature. The solution turned yellow immediately. The reaction mixture was stirred for 6 h and absolute diethyl ether was added. The resulted precipitate was filtered, washed with diethyl ether and dried in a vacuum to furnish the pure product as yellow powder (185 mg, 0.31 mmol) in 91% yield. IR (KBr, cm⁻¹): 2985 (w), 2906 (m), 1622 (m), 1589 (s), 1555 (m), 1464 (s), 1382 (m), 1255 (m), 1216 (m), 791 (m), 757 (s). MALDI-TOF: calcd for C₂₀H₂₀Cl₂CoN₂m/z 417.0, found m/z 382.1 (M–Cl)⁺. Anal. calcd for C₂₀H₂₀Cl₂CoN₂: C 57.44, H 4.82, N 6.70. Found: C 57.62, H 5.00, N 6.77.

2-(1-(2,6-Diethylphenylimino)propylidene)quinolylcobalt dichloride C2. Using the same procedure as for the synthesis of C1, C2 was obtained in 92% yield. IR (KBr, cm⁻¹): 2971 (w), 1610 (m), 1588 (s), 1553 (m), 1446 (s), 1381 (m), 1261 (m), 1218 (m), 767 (m), 756 (s). MALDI-TOF: calcd for C₂₂H₂₄Cl₂CoN₂m/z 445.1, found m/z 410.1 (M–Cl)⁺. Anal. calcd for (C₂₂H₂₄Cl₂CoN₂)₂: C 59.21, H 5.42, N 6.28. Found: C 59.32, H 5.44, N 6.27.

2-(1-(2,6-Diisopropylphenylimino)propylidene)quinolyl-cobalt dichloride C3. Using the same procedure as for the synthesis of C1, C3 was obtained in 89% yield. IR (KBr, cm⁻¹): 2963 (w), 1603 (m), 1587 (s), 1557 (m), 1461 (s), 1385 (m), 1308 (m), 1218 (m), 788 (m), 762 (s). MALDI-TOF: calcd for C₂₄H₂₈Cl₂CoN₂m/z 473.1, found m/z 438.1 (M–Cl)⁺. Anal. calcd for C₂₄H₂₈Cl₂CoN₂: C 60.77, H 5.95, N 5.91. Found: C 60.62, H 6.00, N 5.77.

2-(1-(2,4,6-Trimethylphenylimino)propylidene)quinolyl-cobalt dichloride C4. Using the same procedure as for the synthesis of C1, C4 was obtained in 81% yield. IR (KBr, cm⁻¹): 2980 (w), 1615 (m), 1554 (s), 1509 (m), 1464 (s), 1346 (m), 1217 (m), 1145 (m), 830 (m), 758 (s). MALDI-TOF: calcd for C₂₁H₂₂Cl₂CoN₂m/z 431.0, found m/z 396.1 (M–Cl)⁺. Anal. calcd for C₂₁H₂₂Cl₂CoN₂: C 58.35, H 5.13, N 6.48. Found: C 58.62, H 5.00, N 6.77.

2-(1-(2,6-Diethyl-4-methylphenylimino)propylidene) quinolylcobalt dichloride C5. Using the same procedure as for the synthesis of C1, C5 was obtained in 79% yield. IR (KBr, cm⁻¹): 2971 (w), 2903 (m), 1617 (m), 1588 (s), 1553 (m), 1446 (s), 1381 (m), 1261 (m), 1218 (m), 795 (m), 756 (s). MALDI-TOF: calcd for C₂₃H₂₆Cl₂CoN₂m/z 459.1, found m/z 424.1 (M–Cl)⁺. Anal. calcd for C₂₃H₂₆Cl₂CoN₂: C 60.01, H 5.69, N 6.09. Found: C 59.62, H 5.60, N 6.07.

2-(1-(2,6-Dichlorophenylimino)propylidene)quinolylcobalt dichloride C6. Using the same procedure as for the synthesis of C1, C6 was obtained in 82% yield. IR (KBr, cm⁻¹): 3067 (w), 1618 (m), 1583 (s), 1559 (m), 1436 (s), 1386 (m), 1226 (m), 1205 (m), 778 (m), 762 (s). MALDI-TOF: calcd for C₁₈H₁₄Cl₄CoN₂m/z 456.9, found m/z 421.9 (M–Cl)⁺. Anal. calcd for C₁₈H₁₄Cl₄CoN₂: C 47.09, H 3.07, N 6.10. Found: C 47.02, H 3.00, N 6.17.

4.3 General procedure for ethylene dimerization and polymerization

Ethylene dimerization or/and polymerization at 10 atm of ethylene pressure was carried out in a stainless steel autoclave (250 mL capacity) equipped with a mechanical stirrer and a temperature controller. The toluene solution of the catalytic precursor and toluene (the total volume was 100 mL) were added into the autoclave under nitrogen atmosphere. The required amount of co-catalyst then was injected into the reactor via a syringe. The ethylene pressure was tuned to 10 atm, and maintained at this level by constant feeding of ethylene at the desired reaction temperature. After the reaction mixture was stirred for the desired period, the mixture was cooled to room temperature by the ice bath, then the pressure was released. A small amount of the reaction solution was collected, which was then analyzed by gas chromatography (GC) for determining the composition and mass distribution of oligomers obtained. While the reaction solution was quenched with 5% hydrochloride acid in ethanol, the precipitated polymer was collected by filtration, and was adequately washed with ethanol and water, and was then dried in a vacuum until constant weight.

4.4 Crystal structure determinations

Single-crystal X-ray diffraction study for C2 and C3 was carried out on a Rigaku RAXIS Rapid IP diffractometer with graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å). 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.¹⁹Crystal data and processing parameters for C2 and C3 is collected in Table 4.

Table 4 Crystal data and structure refinement for C2 and C3

	C2	C3
Empirical formula	C22H24Cl2CoN2	C24H28Cl2CoN2
Formula weight	446.26	474.31
Crystal color	Yellow	Blue
T/K	173(2)	173(2)
λ/Å	0.71073	0.71073
Crystal system	Monoclinic	Monoclinic
Space group	P21/n	P21/n
a/Å	11.337(2)	10.125(2)
b/Å	15.712(3)	16.885(3)
c/Å	11.611(2)	13.533(3)
β/°	95.49(3)	90.01(3)
V/Å^3	2058.6(7)	2313.7(8)
Z	4	4
D c/Mg m^−3	1.440	1.362
μ/mm^−1	1.102	0.985
F(000)	924	988
Crystal size/mm	0.13 × 0.12 × 0.03	0.20 × 0.20 × 0.20
θ range/°	2.40–27.45	2.35–27.51
Limiting indices	−13 ≤ h ≤ 14	−13 ≤ h ≤ 13
	−20 ≤ k ≤ 17	−21 ≤ k ≤ 15
	−–15 ≤ l ≤ 15	−16 ≤ l ≤ 17
Completeness to θ (%)	99.7 (θ = 27.45)	98.7 (θ = 27.51)
R int	0.0500	0.0595
Absorption correction	Empirical	Empirical
Data/restraints/parameters	4682/82/272	5245/42/282
Goodness-of-fit on F^2	1.200	1.113
Final R indices [I > 2σ(I)]	R 1 = 0.0574, wR2 = 0.1313	R 1 = 0.0537, wR2 = 0.1082
R indices (all data)	R 1 = 0.0616, wR2 = 0.1336	R 1 = 0.0595, wR2 = 0.1117
Largest diffraction peak and hole/e Å^−3	0.402 and −0.353	0.423 and −0.415

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Acknowledgements

This work is supported by MOST 863 program no. 2009AA033601.

References

1. (a) B. L. Small, M. Brookhart and A. M. A. Bennett, J. Am. Chem. Soc., 1998, 120, 4049; (b) G. J. P. Britovsek, V. C. Gibson, B. S. Kimberley, P. J. Maddox, S. J. McTavish, G. A. Solan, A. J. P. White and D. J. Williams, Chem. Commun., 1998, 849.
2. (a) G. J. P. Britovsek, V. C. Gibson and D. F. Wass, Angew. Chem., Int. Ed., 1999, 38, 428; (b) S. D. Ittel, L. K. Johnson and M. Brookhart, Chem. Rev., 2000, 100, 1169; (c) V. C. Gibson and S. K. Spitzmesser, Chem. Rev., 2003, 103, 283; (d) V. C. Gibson, C. Redshaw and G. A. Solan, Chem. Rev., 2007, 107, 1745; (e) C. Bianchini, G. Giambastiani, I. G. Rios, G. Mantovani, A. Meli and A. M. Segarra, Coord. Chem. Rev., 2006, 250, 1391; (f) C. Bianchini, G. Giambastiani, L. Luconi and A. Meli, Coord. Chem. Rev., 2010, 254, 431; (g) W.-H. Sun, S. Zhang and W. Zuo, C. R. Chim., 2008, 11, 307; (h) S. Jie, W.-H. Sun and T. Xiao, Chin. J. Polym. Sci., 2010, 28, 299.
3. (a) B. L. Small and M. Brookhart, J. Am. Chem. Soc., 1998, 120, 7143; (b) G. J. P. Britovsek, M. Bruce, V. C. Gibson, B. S. Kimberley, P. J. Maddox, S. Mastroianni, S. J. McTavish, C. Redshaw, G. A. Solan, S. Strömberg, A. J. P. White and D. J. Williams, J. Am. Chem. Soc., 1999, 121, 8728; (c) G. J. P. Britovsek, S. Mastroianni, G. A. Solan, S. P. D. Baugh, C. Redshaw, V. C. Gibson, A. J. P. White, D. J. Williams and M. R. J. Elsegood, Chem.–Eur. J., 2000, 6, 2221; (d) E. P. Talsi, D. E. Babushkin, N. V. Semikolenova, V. N. Zudin, V. N. Panchenko and V. A. Zakharov, Macromol. Chem. Phys., 2001, 202, 2046; (e) Z. Ma, W.-H. Sun, Z. L. Li, C. X. Shao, Y. L. Hu and X. H. Li, Polym. Int., 2002, 51, 994; (f) Y. Chen, C. Qian and J. Sun, Organometallics, 2003, 22, 1231; (g) I. S. Paulino and U. Schuchardt, J. Mol. Catal. A: Chem., 2004, 211, 55; (h) Z. Zhang, S. Chen, X. Zhang, H. Li, Y. Ke, Y. Lu and Y. Hu, J. Mol. Catal. A: Chem., 2005, 230, 1; (i) J.-Y. Liu, Y. Zheng, Y.-G. Li, L. Pan, Y.-S. Li and N.-H. Hu, J. Organomet. Chem., 2005, 690, 1233.
4. (a) V. C. Gibson, M. J. Humphries, K. P. Tellmann, D. F. Wass, A. J. P. White and D. J. Williams, Chem. Commun., 2001, 2252; (b) G. J. P. Britovsek, G. K. B. Clentsmith, V. C. Gibson, D. M. L. Goodgame, S. J. McTavish and Q. A. Pankhurst, Catal. Commun., 2002, 3, 207; (c) K. P. Bryliakov, N. V. Semikolenova, V. A. Zakharov and E. P. Talsi, Organometallics, 2004, 23, 5375; (d) K. P. Bryliakov, N. V. Semikolenova, V. N. Zudin, V. A. Zakharov and E. P. Talsi, Catal. Commun., 2004, 5, 45; (e) J. Cámpora, A. M. Naz, P. Palma, E. Álvarez and M. L. Reyes, Organometallics, 2005, 24, 4878; (f) M. W. Bouwkamp, E. Lobkovsky and P. J. Chirik, J. Am. Chem. Soc., 2005, 127, 9660; (g) S. C. Bart, K. Chlopek, E. Bill, M. W. Bouwkamp, E. Lobkovsky, F. Neese, K. Wieghardt and P. J. Chirik, J. Am. Chem. Soc., 2006, 128, 13901; (h) C. Wallenhorst, G. Kehr, H. Luftmann, R. Fröhlich and G. Erker, Organometallics, 2008, 27, 6547; (i) R. J. Trovitch, E. Lobkovsky and P. J. Chirik, J. Am. Chem. Soc., 2008, 130, 11631; (j) V. L. Cruz, J. Ramos, J. Martínez-Salazar, S. Gutiérrez-Oliva and A. Toro-Labbé, Organometallics, 2009, 28, 5889; (k) R. Raucoules, T. Bruin, P. Raybaud and C. Adamo, Organometallics, 2009, 28, 5358; (l) K. P. Bryliakov, E. P. Talsi, N. V. Semikolenova and V. A. Zakharov, Organometallics, 2009, 28, 3225; (m) A. C. Bowman, C. Milsmann, C. C. H. Atienza, E. Lobkovsky, K. Wieghardt and P. J. Chirik, J. Am. Chem. Soc., 2010, 132, 1676; (n) A. C. Bowman, C. Milsmann, E. Bill, E. Lobkovsky, T. Weyhermüller, K. Wieghardt and P. J. Chirik, Inorg. Chem., 2010, 49, 6110; (o) A. M. Tondreau, C. Milsmann, A. D. Patrick, H. M. Hoyt, E. Lobkovsky, K. Wieghardt and P. J. Chirik, J. Am. Chem. Soc., 2010, 132, 15046; (p) C. C. H. Atienza, A. C. Bowman, E. Lobkovsky and P. J. Chirik, J. Am. Chem. Soc., 2010, 132, 16343.
5. (a) R. Cowdell, C. J. Davies, S. J. Hilton, J.-D. Maréchal, G. A. Solan, O. Thomas and J. Fawcett, Dalton Trans., 2004, 3231; (b) A. R. Karama, E. L. Cataría, F. López-Linaresa, G. Agrifoglioa, C. L. Albanoa, A. Díaz-Barriosa, T. E. Lehmanna, S. V. Pekerara, L. A. Albornoza, R. Atencioa, T. Gonzáleza, H. B. Ortegab and P. Joskowicsb, Appl. Catal., A, 2005, 280, 165; (c) A. Karama, R. Tenia, M. Martínez, F. López-Linares, C. Albano, A. Diaz-Barrios, Y. Sánchez, E. Catarí, E. Casas, S. Pekerar and A. Albornoz, J. Mol. Catal. A: Chem., 2007, 265, 127; (d) B. L. Small, R. Rios, E. R. Fernandez and M. J. Carney, Organometallics, 2007, 26, 1744; (e) K. Tenza, M. J. Hanton and A. M. Z. Slawin, Organometallics, 2009, 28, 4852.
6. (a) W.-H. Sun, P. Hao, S. Zhang, Q. Shi, W. Zuo, X. Tang and X. Lu, Organometallics, 2007, 26, 2720; (b) Y. Chen, P. Hao, W. Zuo, K. Gao and W.-H. Sun, J. Organomet. Chem., 2008, 693, 1829; (c) L. Xiao, R. Gao, M. Zhang, Y. Li, X. Cao and W.-H. Sun, Organometallics, 2009, 28, 2225.
7. W.-H. Sun, P. Hao, G. Li, S. Zhang, W. Wang, J. Yi, M. Asma and N. Tang, J. Organomet. Chem., 2007, 692, 4506.
8. (a) W.-H. Sun, S. Jie, S. Zhang, W. Zhang, Y. Song and H. Ma, Organometallics, 2006, 25, 666; (b) S. Jie, S. Zhang, W.-H. Sun, X. Kuang, T. Liu and J. Guo, J. Mol. Catal. A: Chem., 2007, 269, 85; (c) S. Jie, S. Zhang, K. Wedeking, W. Zhang, H. Ma, X. Lu, Y. Deng and W.-H. Sun, C. R. Chim., 2006, 9, 1500; (d) S. Jie, S. Zhang and W.-H. Sun, Eur. J. Inorg. Chem., 2007, 5584; (e) M. Zhang, W. Zhang, T. Xiao, J.-F. Xiang, X. Hao and W.-H. Sun, J. Mol. Catal. A: Chem., 2010, 320, 92.
9. (a) M. Zhang, P. Hao, W. Zuo, S. Jie and W.-H. Sun, J. Organomet. Chem., 2008, 693, 483; (b) M. Zhang, R. Gao, X. Hao and W.-H. Sun, J. Organomet. Chem., 2008, 693, 3867.
10. (a) A. Köppl and H. G. Alt, J. Mol. Catal. A: Chem., 2000, 154, 45; (b) G. J. P. Britovsek, S. P. D. Baugh, O. Hoarau, V. C. Gibson, D. Wass, A. J. P. White and D. J. Williams, Inorg. Chim. Acta, 2003, 345, 279; (c) V. C. Gibson, C. M. Halliwell, N. J. Long, P. J. Oxford, A. M. Smith, A. J. P. White and D. J. Williams, Dalton Trans., 2003, 918; (d) K. Wang, K. Wedeking, W. Zuo, D. Zhang and W.-H. Sun, J. Organomet. Chem., 2008, 693, 1073.
11. (a) S. Zhang, I. Vystorop, Z. Tang and W.-H. Sun, Organometallics, 2007, 26, 2456; (b) S. Zhang, W.-H. Sun, X. Kuang, I. Vystorop and J. Yi, J. Organomet. Chem., 2007, 692, 5307.
12. (a) R. Gao, K. Wang, Y. Li, F. Wang, W.-H. Sun, C. Redshaw and M. Bochmann, J. Mol. Catal. A: Chem., 2009, 309, 166; (b) R. Gao, Y. Li, F. Wang, W.-H. Sun and M. Bochmann, Eur. J. Inorg. Chem., 2009, 4149.
13. S. Zhang, W.-H. Sun, T. Xiao and X. Hao, Organometallics, 2010, 29, 1168.
14. (a) T. V. Laine, K. Lappalainen, J. Liimatta, E. Aitolal, B. Löfgren and M. Leskelä, Macromol. Rapid Commun., 1999, 20, 487; (b) L. Wang, W.-H. Sun, Z. Li, L. Han, Y. Hu, C. He and C. Yang, J. Organomet. Chem., 2002, 650, 59; (c) C. Bianchini, G. Mantovani, A. Meli and F. Migliacci, Organometallics, 2003, 22, 2545; (d) C. Bianchini, G. Giambastiani, G. Mantovani, A. Meli and D. Mimeau, J. Organomet. Chem., 2004, 689, 1356; (e) W.-H. Sun, X. Tang, T. Gao, B. Wu, W. Zhang and H. Ma, Organometallics, 2004, 23, 5037; (f) C. Bianchini, D. Gatteschi, G. Giambastiani, I. G. Rios, A. Ienco, F. Laschi, C. Mealli, A. Meli, L. Sorace, A. Toti and F. Vizza, Organometallics, 2007, 26, 726; (g) M. Tanabiki, Y. Sunada and H. Nagashima, Organometallics, 2007, 26, 6055; (h) V. Rosa, S. A. Carabineiro, T. Avilés, P. T. Gomes, R. Welter, J. M. Campos and M. R. Ribeiro, J. Organomet. Chem., 2008, 693, 769.
15. (a) R. J. Butcher and E. Sinn, Inorg. Chem., 1977, 16, 2334; (b) T. V. Laine, M. Klinga and M. Leskelä, Eur. J. Inorg. Chem., 1999, 959; (c) F. Speiser, P. Braunstein, L. Saussine and R. Welter, Inorg. Chem., 2004, 43, 1649; (d) P. Chavez, I. Rios, A. Kermagoret, R. Pattacini, A. Meli, C. Bianchini, G. Giambastiani and P. Braunstein, Organometallics, 2009, 28, 1776; (e) W.-H. Sun, W. Zhang, T. Gao, X. Tang, L. Chen, Y. Li and X. Jin, J. Organomet. Chem., 2004, 689, 917.
16. (a) D. Guo, L. Han, T. Zhang, W.-H. Sun, T. Li and X. Yang, Macromol. Theory Simul., 2002, 11, 1006; (b) T. Zhang, D. Guo, S. Jie, W.-H. Sun, T. Li and X. Yang, J. Polym. Sci., Part A: Polym. Chem., 2004, 42, 4765.
17. M. Atiqullah, H. Hammawa and H. Hamid, Eur. Polym. J., 1998, 34, 1511.
18. (a) E. Y. -X. Chen and T. J. Marks, Chem. Rev., 2000, 100, 1391; (b) X. Tang, D. Zhang, S. Jie, W.-H. Sun and J. Chen, J. Organomet. Chem., 2005, 690, 3918; (c) W. Zhang, W.-H. Sun, S. Zhang, J. Hou, K. Wedeking, S. Schultz, R. Fröhlich and H. Song, Organometallics, 2006, 25, 1961; (d) W. Zhang, W.-H. Sun, X. Tang, T. Gao, S. Zhang, P. Hao and J. Chen, J. Mol. Catal. A: Chem., 2007, 265, 159.
19. Sheldrick, G. M. SHELXTL-97, Program for the Refinement of Crystal Structures; University of Göttingen: Germany, 1997.

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Footnote

† Electronic Supplementary Information (ESI) available: CCDC reference numbers 805826 and 805827 for crystallographic data of complexes C2 and C3. See http://dx.doi.org/10.1039/c1cy00028d

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