Amine influence in vanadium-based ethylene polymerisation pro-catalysts bearing bis(phenolate) ligands with ‘pendant’ arms

Abstract

Two families of vanadium complexes bearing diphenolate ligands with different ‘pendant’ arms have been screened under various conditions for the polymerisation behaviour of ethylene. The presence of a bound amine arm was found to favour enhanced thermal stability.

---

Introduction

Non-metallocene based pro-catalysts for α-olefin polymerisation, utilising either early or late transition metals with various combinations of ancillary ligands, continue to attract considerable academic and industrial interest.¹Vanadium-based polymerisation systems date back to the 1950s, and such systems achieved notably success in the heterogeneous arena.² However, homogeneous systems were less attractive, primarily due to low activities; the ease of reduction of the metal centre was problematic.³ A number of re-activating agents such as trichloroethylacetate (ETA) have been deployed, which help to overcome this problem.⁴ It is also now becoming apparent that the co-catalyst of choice (for non-supported systems) is based on a chloroaluminium reagent.⁵ Given all of this, vanadium is now emerging as a promising candidate, and a number of highly active, thermally stable systems have recently been reported. Notable structure–activity trends have been highlighted when using a number of ligand sets,^5,6 for example organoimido complexes.⁷ The majority of such systems though tend to utilize chelating ligands binding through oxygen, nitrogen or a combination of both, examples include N,O-chelates such as phenoxyimines,⁸ and β-enaminoketonato,⁹N,N-chelates such as (2-anilidomethyl)pyridine¹⁰ and poly(aryloxides) such as C or N-capped tripodal ligands¹¹ and calixarenes.¹² We have also previously probed the use of amine bis(phenolate) ligands of the type [ONNO^RR]H₂2 (see Chart 1) and found that resulting vanadium(II–V) pro-catalysts were capable of ethylene polymerisation, using EtAlCl₂ as co-catalyst, with activities in the region of 300 g mmol⁻¹ h bar.¹³ Such amine bis(phenolate) ligands were initially used in group 4 based polymerisation catalysis by Kolet al.¹⁴ Herein, we extended these studies to other co-catalysts including dimethylaluminium chloride (DMAC), methylaluminoxane (MAO) and trimethylaluminium (TMA), all with or without the re-activator trichloroethylacetate (ETA) present. Furthermore, these studies were extended to the related ligand set [ONNO^RR]H₂2, which enables the influence of the amine group in [ONNO^RR]H₂2 to be probed.

Chart 1 Ligands used in this study (R = Me, ^tBu).

Results and discussion

Pro-catalysts 1, 2 and 3, 4 (Chart 2) are readily available in high yields (≥ 80%) via the reaction of VO(OⁱPr)₃ with the ligands [ONNO^RR]H₂2 or [ONO^RR]H₂2, respectively. The complexes are obtained as a mixture of two isomers (see Chart 2), as evidenced by ⁵¹V NMR spectroscopy: cis refers to the isomer in which the oxo ligand is located in the cis position to the tripodal N atom. The structure of mononuclear ciscis-1 has previously been reported.¹³ It has also been possible to grow single crystals of ciscis-3 from a saturated toluene–pentane solution. The molecular structure is shown in Fig. 1, with selected bond lengths and angles given in the caption. Crystallographic data are presented in Table 1. The geometry at vanadium is best described as distorted trigonal bipyramidal with O(1) and N(1) apical. The oxo group is cis to N(1), for which the V(1)–N(1) distance is 2.248(4) Å, similar to that observed for the tripodal nitrogen in cis-1 [2.3773(16) Å]. The V(1)–O(1) distance [1.782(3) Å] and V(1)–O(1)–C(4) angle [125.6(3)°] are indicative of the presence of π-donor character. Interestingly, from ethanol solution, this penta-coordinate complex can still be isolated.

Chart 2 Pro-catalysts used in this study.

Fig. 1 ORTEP drawing of the molecular structure of cis-3 showing 50% probability ellipsoids. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (°): V(1)–O(1) 1.782(3), V(1)–O(2) 1.821(3), V(1)–O(3) 1.839(3), V(1)–O(4) 1.578(3), V(1)–N(1) 2.248(4); O(1)–V(1)–N(1) 168.40(15), O(2)–V(1)–O(3) 130.88(15), O(3)–V(1)–O(4) 114.29(18), V(1)–O(2)–C(7) 135.5(3), V(1)–O(3)–C(16) 139.4(3).

Table 1 Crystallographic data, data collection and refinement parameters for complex 3

	3
Chemical formula	C24H34NO4V
Formula weight	451.46
Crystal system	Monoclinic
Space group	P21/c
a/Å	8.4832(12)
b/Å	11.5025(16)
c/Å	24.140(3)
α/°	90.0
β/°	94.873(12)
γ/°	90.0
V/Å^3	2347.0(6)
Z	4
D c/g cm^−3	1.278
μ(Mo-Kα)/mm^−1	0.451
F(000)	960
θ range/°	2.83 to 25.35
Measured reflections	16 030
Unique reflections/Rint	4289/0.1848
Parameters/restraints	278/0
Final R indices [I > 2σ(I)]	R 1 = 0.0681
	wR2 = 0.1089
Final R indices all data	R 1 = 0.1833
	wR2 = 0.1377
Goodness of fit	0.959
Δρmax, Δρmin	0.396 and −0.512

---

A comparison of the main geometrical parameters associated with cis-1 and cis-3 is presented in Chart 3. The presence of the additional nitrogen donor in pseudo octahedral cis-1 results in a lengthening of the bonds around the metal centre (except for the V–OnPr bond), which is consistent with the higher coordination number in 1vs.3. The overall structural features compare well with other structurally characterized trigonal bipyramidal oxo-alkoxo vanadium complexes with ONO type ligands.¹⁴

Chart 3 Selected geometrical parameters of cis-1 and cis-3.

Clearly, the difference between the structures of the pro-catalysts 1, 2 and 3, 4 is the presence of the NMe₂ side arm in 1 and 2, which results in pseudo octahedral coordination at vanadium. To ascertain how the presence of this bound amine affects the polymerisation catalysis, pro-catalysts 1, 2 and 3, 4 have all been screened under the same conditions, and a number of the screening parameters have been systematically varied. Screening results are presented in Table 2 (for 1 and 2), Table 3 (for 3 and 4) and Table 4 (for low molecular weight material from 3). Analysis of the results in Table 2 reveals that only the co-catalyst DMAC affords polymer; as for related systems,¹³ use of MAO or TMA (runs 6–9 and 31–34) yielded no polymer. Lifetime studies at 45 °C using 1 or 2, in combination with DMAC (and ETA), revealed a steady decrease in the observed activity with time over 30 min. As shown in Chart 4, activities for 1 (runs 1–4) were somewhat higher than those for 2 (runs 18–21). For 1 and 2, there was little change in polymer molecular weight over time, and in both cases, the range of PDIs measured was within the range 2.9–5.5. On changing the temperature, it was observed that at 25 °C, the activity of 1 exceeded that of 2 (run 5 vs. 30), whereas at 60 °C, 2 out-performed 1 (run 16 vs. 27). The activities of 1 and 2 were comparable at 80 °C (runs 17 and 28). Increasing the [Al] : [V] ratio (Chart 5) at 25 °C for 1, led to a gradual increase in activity which peaked at 3000 equivalents of DMAC, whereas for 2 at 0 °C the activity peaked at 2000 equivalents of DMAC.

Table 2 Polymerisation runs using pro-catalysts 1 and 2

Run	Pro-catalyst/μmol	Co-catalyst	[Al]/[V]	T/°C	t/min	Yield PE/g	Activity^b	M w ^c	M n ^d	PDI^e
1 bar ethylene Schlenk tests carried out in toluene (50 mL) in the presence of ETA (0.05 mL), reaction was quenched with dilute HCl, washed with methanol (50 mL) and dried for 12 h at 80 °C.a Without ETA.b g mmol^−1 h bar (×10^3).c Weight average molecular weight (×10^3).d Number average molecular weight (×10^3).e Polydispersity index.
1	1 (0.50)	DMAC	4000	45	5	1.11	26.5	285	80/9	3.5
2	1 (0.50)	DMAC	4000	45	10	1.91	22.9	370	115	3.2
3	1 (0.50)	DMAC	4000	45	20	2.74	16.4	347	79.8	4.3
4	1 (0.50)	DMAC	4000	45	30	2.61	10.5	311	66/5	4.7
5^a	1 (0.50)	DMAC	4000	25	15	0.30	2.4	—	—	—
6	1 (0.50)	MAO	4000	25	15	0.00	0	—	—	—
7^a	1 (0.50)	MAO	4000	25	15	0.00	0	—	—	—
8	1 (0.50)	TMA	4000	25	15	0.00	0	—	—	—
9^a	1 (0.50)	TMA	4000	25	15	0.00	0	—	—	—
10	1 (0.50)	DMAC	1000	25	15	0.65	5.2	—	—	—
11	1 (0.50)	DMAC	2000	25	15	0.76	6.0	—	—	—
12	1 (0.50)	DMAC	3000	25	15	0.99	7.9	—	—	—
13	1 (0.50)	DMAC	5000	25	15	0.77	6.1	—	—	—
14	1 (0.50)	DMAC	4000	0	15	0.08	0.7	—	—	—
15	1 (0.50)	DMAC	4000	45	15	1.34	10.7	—	—	—
16	1 (0.50)	DMAC	4000	60	15	1.51	12.1	—	—	—
17	1 (0.50)	DMAC	4000	80	15	2.16	17.1	—	—	—
18	2 (0.50)	DMAC	4000	45	5	0.56	13.5	392	71.4	5.5
19	2 (0.50)	DMAC	4000	45	10	0.86	10.3	394	98/7	4.0
20	2 (0.50)	DMAC	4000	45	19	2.13	13.4	410	142	2.9
21	2 (0.50)	DMAC	4000	45	30	1.33	5.3	461	126	3.7
22	2 (0.50)	DMAC	1000	0	15	0.80	6.4	—	—	—
23	2 (0.50)	DMAC	2000	0	15	1.03	8.2	—	—	—
24	2 (0.50)	DMAC	3000	0	15	0.80	6.4	—	—	—
25	2 (0.50)	DMAC	5000	0	15	0.48	3.8	—	—	—
26	2 (0.50)	DMAC	4000	45	15	1.00	8.0	—	—	—
27	2 (0.50)	DMAC	4000	60	15	1.91	15.3	—	—	—
28	2 (0.50)	DMAC	4000	80	15	2.22	17.8	—	—	—
29	2 (0.50)	DMAC	4000	25	15	0.93	7.5	—	—	—
30^a	2 (0.50)	DMAC	4000	25	15	0.21	1.7	—	—	—
31	2 (0.50)	MAO	3921	25	15	0.00	0	—	—	—
32^a	2 (0.50)	MAO	3921	25	15	0.00	0	—	—	—
33	2 (0.50)	TMA	4000	25	15	0.00	0	—	—	—
34^a	2 (0.50)	TMA	4000	25	15	0.00	0	—	—	—

---

Table 3 Polymerisations runs using pro-catalysts 3 and 4

Run	Pro-catalyst/μmol	Co-catalyst	[Al]/[V]	T/°C	t/min	Yield PE/g	Activity^b	M w ^c	M n ^d	PDI^e
1 bar ethylene Schlenk tests carried out in toluene (50 mL) in the presence of ETA (0.05 mL), reaction was quenched with dilute HCl, washed with methanol (50 mL) and dried for 12 h at 80 °C.a Without ETA.b g mmol^−1 h bar (×10^3).c Weight average molecular weight (×10^3).d Number average molecular weight (×10^3).e Polydispersity index.f Sample also contained low molecular weight (see Table 4).
35	3 (0.50)	DMAC	4000	25	15	0.99	7.9	377^f	138^f	2.7
36	3 (0.05)	DMAC	40 000	25	15	0.03	2.4	—	—	—
37^a	3 (0.50)	DMAC	4000	25	15	0.05	4	790^f	358^f	2.2
38	3 (0.50)	MAO	3921	25	15	0	0	—	—	—
39^a	3 (0.50)	MAO	3921	25	15	0	0	—	—	—
40	3 (0.50)	TMA	4000	25	15	0	0	—	—	—
41^a	3 (0.50)	TMA	4000	25	15	0	0	—	—	—
42	3 (0.50)	DMAC	1000	25	15	0.07	0.6	402^f	146^f	2.8
43	3 (0.50)	DMAC	2000	25	15	0.41	3.3	550^f	245^f	2.2
44	3 (0.50)	DMAC	3000	25	15	0.76	6.1	533^f	213^f	2.5
45	3 (0.50)	DMAC	5000	25	15	1.17	9.4	354	122	2.9
46	3 (0.50)	DMAC	4000	0	15	0.01	0.08	456^f	127^f	3.6
47	3 (0.50)	DMAC	4000	45	15	1.41	11.3	131	27	4.9
48	3 (0.50)	DMAC	4000	60	15	0.97	7.8	59.2	11/6	5.1
49	3 (0.50)	DMAC	4000	80	15	0.26	2.1	327^f	65.1^f	5.0
50	3 (0.50)	DMAC	4000	25	15	0.85	6.1	559^f	261^f	2.1
51	3 (0.50)	DMAC	4000	45	5	0.95	22.8	161	35.2	4.6
52	3 (0.50)	DMAC	4000	45	10	1.42	17.0	131	25.3	5.2
53	3 (0.50)	DMAC	4000	45	20	2.62	15.7	190	42/9	4.4
54	3 (0.50)	DMAC	4000	45	30	2.61	10.4	217	38	5.7
55^a	4 (0.50)	DMAC	4000	25	15	0.06	0.5	1260	489	2.6
56	4 (0.50)	MAO	3921	25	15	0.00	0	—	—	—
57^a	4 (0.50)	MAO	3921	25	15	0.00	0	—	—	—
58	4 (0.50)	TMA	4000	25	15	0.00	0	—	—	—
59^a	4 (0.50)	TMA	4000	25	15	0.00	0	—	—	—
60	4 (0.50)	DMAC	1000	25	15	0.27	1.3	654	216	3.0
61	4 (0.50)	DMAC	2000	25	15	0.55	2.6	776	198	3.9
62	4 (0.50)	DMAC	1000	0	15	0.18	1.4	589	220	2.7
63	4 (0.50)	DMAC	2000	0	15	0.59	4.7	514	74/7	6.9
64	4 (0.50)	DMAC	3000	0	15	0.72	5.8	602	244	2.7
65	4 (0.50)	DMAC	5000	0	15	0.90	7.2	384	26/6	14
66	4 (0.50)	DMAC	4000	45	15	1.32	10.6	335	116	2.9
67	4 (0.50)	DMAC	4000	60	15	0.95	7.6	82.3	21/6	3.8
68	4 (0.50)	DMAC	4000	80	15	0.00	0	—	—	—
69	4 (0.50)	DMAC	4000	45	5	0.42	10.1	479	127	3.8
70	4 (0.50)	DMAC	4000	45	10	0.60	7.2	584	145	4.0
71	4 (0.50)	DMAC	4000	45	20	0.95	5.7	500	119	4.2
72	4 (0.50)	DMAC	4000	45	30	1.03	4.1	440	57.5	7.6

---

Table 4 Low molecular weight material from runs in Table 3

Run	M w ^a	M n ^b	PDI^c
a Weight average molecular weight (×10^3). b Number average molecular weight (×10^3). c Polydispersity index.
35	361	33.2	11
37	689	47.5	15
42	393	79.8	4.9
43	459	23.4	20
44	432	18.4	23
46	456	127	3.6
49	327	65.1	2.8
50	559	261	2.1

---

Chart 4 Lifetime activities for pro-catalysts 1–4.

Chart 5 Influence of co-catalyst loading on polymerisation activity for pro-catalysts 1–4.

Analysis of Table 3 reveals a similar trend for the lifetime studies at 45 °C, with activities for 3 (runs 51–54) being higher that those of 4 (runs 69–72) over 30 min. Molecular weights obtained for 3 were somewhat lower that those obtained using 4. The activities of 3 and 4 were comparable at 25 °C (runs 43 and 61) and 60 °C (runs 48 and 67), whereas at 0 °C 4 > 3 (runs 46 and 62–65) and at 80 °C 3 > 4 (runs 49 and 68). On changing the temperature, it was observed that the activities of 3 and 4 peaked at 45 °C (runs 46–49 and 65–68). In each case, the highest molecular weight was observed at 0 °C, though in the case of 4, the PDI had risen to 14. Such broad PDIs suggest that competing processes were taking place leading to loss of single-site catalysis. Increasing the [Al] : [V] ratio at 25 °C for 3, led to a gradual increase in activity over the range 1000–5000 equivalents of DMAC, and similarly for 4 at 0 °C.

Comparison between the two sets of pro-catalysts, i.e.Table 2vs.Table 3, reveals that at 25 °C, 1 is much more active than 3 for smaller [Al] : [V] ratio, whereas at a ratio of 5000 : 1, 3 gives a more active system (runs 10–13 and 42–45). At 45 °C, 1 and 3 gave comparable activities, particularly after 30 min (runs 4 and 54), whereas 3 (run 47) afforded an activity a little higher than that observed for 4 (run 66). At both 60 °C and 80 °C, the amine-bound pro-catalysts 1 and 2 were found to be far superior in terms of activity (runs 16, 17 and 27, 28 vs. 48, 49 and 67, 68). Highest recorded activities (22 000–26 000) were observed for the methyl-substituted pro-catalysts 1 and 3, when using 4000 equivalents of DMAC at 45 °C (runs 1, 2, 51).

Given the activity trends noted above for increasing [V] : [Al], it can be concluded that the absence of ETA is somewhat detrimental to the observed activity, for example for 1 (runs 5 v 12, 13), for 2 (runs 29 v 30), for 3 (runs 37 v 44, 45) and for 4 (runs 55 v 60, 61).

For a number of runs (see Tables 3 and 4), the analysis of the polymer from pro-catalyst 3 also revealed the presence of low molecular weight material. Despite the solubility of the samples and the lack of problems associated with filtration or chromatography, they exhibited complex shaped distributions (see ESI).† The molecular weight distributions include low molecular weight components; an integration limit that excludes material with molecular weight less than 600 was arbitrarily set (except for run 49).

Conclusion

Synthetic procedures similar to those previously reported for 1 and 2 allow access to pro-catalysts 3 and 4. The geometry at vanadium in these new pro-catalysts is distorted trigonal bipyramidal, which contrasts with the pseudo octahedral coordination in 1 and 2 brought about by the presence of the amine arm. The screening results for 1–4 indicate that increased thermal stability (at 60–80 °C) is brought about by the presence of the bound amine in pro-catalysts 1 and 2. At lower temperatures, e.g. 0 °C, pro-catalyst 4 exhibited highest activity. All pro-catalysts afforded high molecular weight, linear (typical melting points by DSC were 132.0 and 139.4 °C for runs 54 and 72, respectively) polyethylene with rather broad PDIs (2.1–14), and in the case of 3, some low molecular weight material was also produced.

Experimental

General methods and instrumentation

All manipulations were carried out using standard Schlenk line or dry box techniques under an atmosphere of argon. Solvents were refluxed and dried over appropriate drying agents under an atmosphere of argon, and collected by distillation. NMR spectra were recorded on Bruker ARX250, DPX300, and Avance500 spectrometers, and referenced internally to residual protio-solvent (¹H) resonances and are reported relative to tetramethylsilane (δ = 0 ppm). Chemical shifts are quoted in δ (ppm). Infrared spectra were prepared as KBr pelets under argon in a glove box and were recorded on a Perkin-Elmer Spectrum GX FT-IR spectrometer. Infrared data are quoted in wavenumber (cm⁻¹). Elemental analyses were performed at the Laboratoire de Chimie de Coordination (Toulouse, France) or by the Service Central de Microanalyses du CNRS at Vernaison (France).

The pro-ligands [ONO^Me2]H₂, [ONO^tBu2]H₂, [ONNO^Me2]H₂ and [ONNO^tBu2]H₂ were prepared by a modification of literature procedures.¹⁵ Complex VO(OiPr)[ONNO^Me2] (1) was prepared according to our previously published procedure.¹⁶

Preparation of VO(OⁱPr)[ONNO^tBu2] (2)

A solution of ligand precursor [ONNO^tBu2]H₂ (644 mg, 1.227 mmol) in toluene (3 mL) was added dropwise to a solution of VO(OⁱPr)₃ (300 mg, 1.228 mmol) in toluene (3 mL) at room temperature. The resulting blue solution was stirred during 12 h. The volatiles were removed under vacuum to afford a brown solid that was washed with cold pentane (2 × 2 mL). Yield: 660 mg (83%). The complex is obtained as a mixture of ciscis-2 and transtrans-2 isomers in a ratio ca. 65 : 35 (according to ¹H and ⁵¹V NMR).

IR: 954 and 980 (νV=O). Anal. calcd for C₃₇H₆₁N₂O₄V: C 68.49, H 9.48, N 4.32. Found: C 68.33, H 9.35, N 4.20. CisCis-2. ¹H NMR (C₆D₆): δ 7.60 (s, 2H, Ar), 7.04 (s, 2H, Ar), 5.75 (sept, J = 5.0 Hz, 1H, CH(CH₃)₂), 3.97 (d, J = 13.5 Hz, 2H, CH₂), 3.50 (d, J = 13.5 Hz, 2H, CH₂), 2.45 (s, 6H, N(CH₃)₂), 2.08 (m, 4H, CH₂), 1.83 (s, 18H, tBu), 1.75 (d, J = 6.0 Hz, 6H, CH(CH₃)₂), 1.70 (s, 18H, tBu). ¹³C NMR (C₆D₆): δ 164.1, 140.5, 134.8, 124.8, 123.2, 123.0 (Ar), 83.8 (CH(CH₃)₂), 62.9 (ArCH₂), 55.7 (CH₂), 54.9 (CH₂), 48.9 (N(CH₃)₂), 35.4 (tBu Cq)), 34.2 (tBu Cq), 35.4 (tBu), 31.0 (tBu), 25.1 (CH(CH₃)₂). ⁵¹V NMR (C₆D₆): δ −509. TransTrans-2. ¹H NMR (C₆D₆): δ 7.50 (s, 2H, Ar), 7.00 (s, 2H, Ar), 7.34 (sept, J = 6.0 Hz, 1H, CH(CH₃)₂), 3.84 (d, J = 13.0 Hz, 2H, CH₂), 3.27 (d, J = 13.3 Hz, 2H, CH₂), 2.76 (s, 6H, N(CH₃)₂), 2.24 (m, 4H, CH₂), 1.93 (s, 18H, tBu), 1.51 (s, 18H, tBu), 0.93 (d, J = 6.0 Hz, 6H, CH(CH₃)₂). ¹³C NMR (C₆D₆): δ 165.8, 141.0, 133.7, 123.4, 122.8, 122.5 (Ar), 83.0 (CH(CH₃)₂), 61.8 (ArCH₂), 57.5 (CH₂), 51.8 (N(CH₃)₂), 51.7 (CH₂)), 35.3 (tBu Cq)), 34.1 (tBu Cq), 31.7 (tBu), 29.8 (tBu), 25.5 (CH(CH₃)₂). ⁵¹V NMR (C₆D₆): δ −423.

Preparation of VO(OⁱPr)[ONO^Me2] (3)

To a toluene solution (2 mL) of 100 mg of VO(OⁱPr)₃ (0.4142 mmol) was added by portions 1 equiv. of [ONO^Me2]H₂ (135 mg, 0.4123 mmol) at room temperature. The resulting dark solution was stirred for 1 day at ambient temperature. The volatiles were removed under vacuum and the solid was washed pentane (3 × 2 mL) and dried under vacuum to give analytically pure material. Yield: 150 mg (80%). Large dark purple crystals of 3 (suitable for X-ray diffraction) were obtained by cooling a toluene–pentane solution of 3. According to ¹H, complex 3 is obtained as the cis-isomer (the trans-isomer is only detected by ⁵¹V NMR and represents less than 3%).

IR: 953 (νV=O). Anal. calcd for C₂₄H₃₄NO₄V: C 63.85, H 7.59, N 3.10. Found: C 64.07, H 7.58, N 3.03. ¹H NMR (C₆D₆): δ 6.87 (s, 2H, Ar), 6.56 (s, 2H, Ar), 5.93 (sept, J = 5.0 Hz, 1H, CH(CH₃)₂), 4.84 (d, J = 13.5 Hz, 2H, CH₂), 3.41 (d, J = 13.5 Hz, 2H, CH₂), 2.66 (br m, 2H, CH₂ⁿPr), 2.36 (s, 6H, CH₃), 2.18 (s, 6H, CH₃), 1.52 (d, J = 6.0 Hz, 6H, CH(CH₃)₂), 1.07 (br m, 2H, CH₂ⁿPr), 0.08 (br t, 3H, CH₃ⁿPr),. ¹³C NMR (C₆D₆): δ 159.0, 131.5, 129.3, 126.8, 124.7, 120.8 (Ar), 85.7 (CH(CH₃)₂), 59.2 (ArCH₂), 49.08 (CH₂CH₂N), 24.6 (Me), 20.5 (Me), 16.6 (CH(CH₃)₂), 13.0 (CH₂CH₂N), 10.8 (CH₃CH₂CH₂N). ⁵¹V NMR (C₆D₆): δ −533.

Preparation of VO(OⁱPr)[ONO^tBu2] (4)

To a toluene solution (2 mL) of 200 mg of VO(OⁱPr)₃ (0.8285 mmol) was added by portions 1 equiv. of [ONO^tBu2]H₂ (410 mg, 0.8270 mmol) at room temperature. The resulting dark solution for 2 days at RT. The volatiles were removed under vacuum. The solid residue was extracted with pentane (5 + 3 mL) and the solution was cooled to −20 °C to afford after drying under vacuum a dark brown-red solid. Yield: 460 mg (90%). 3 is obtained as a mixture of ciscis-4 and transtrans-4 isomers in a ratio ca. 80 : 20 (according to ¹H and ⁵¹V NMR).

IR: 979 (br, νV=O). Anal. calcd for C₃₆H₅₈NO₄V: C 69.76, H 9.43, N 2.26. Found: C 69.82, H 9.49, N 2.24. CisCis-4: ¹H NMR (C₆D₆): δ 7.52 (s, 2H, Ar), 6.94 (s, 2H, Ar), 5.93 (sept, J = 5.0 Hz, 1H, CH(CH₃)₂), 4.90 (d, J = 13.5 Hz, 2H, CH₂), 3.47 (d, J = 13.0 Hz, 2H, CH₂), 2.75 (br m, 2H, CH₂ⁿPr), 1.65 (d, J = 6.0 Hz, 6H, CH(CH₃)₂), 1.63 (s, 18H, tBu), 1.36 (s, 18H, tBu), 1.15 (br m, 2H, CH₂ⁿPr), 0.13 (t, 3H, CH₃ⁿPr). ¹³C NMR (C₆D₆): δ 159.4, 142.6, 135.6, 123.6, 123.5, 121.6 (Ar), 85.5 (CH(CH₃)₂), 60.00 (ArCH₂), 49.14 (CH₂CH₂N), 35.1 (tBu Cq), 34.3 (Cq), 31.6 (tBu), 29.8 (tBu), 25.6 (CH(CH₃)₂), 13.5 (CH₂CH₂N), 11.0 (CH₃CH₂CH₂N). ⁵¹V NMR (C₆D₆): δ −565. TransTrans-4: ¹H NMR (C₆D₆): δ 7.52 (s, 2H, Ar), 6.87 (s, 2H, Ar), 6.20 (sept, J = 5.0 Hz, 1H, CH(CH₃)₂), 4.90 (d, J = 13.5 Hz, 2H, CH₂), 3.47 (d, J = 13.0 Hz, 2H, CH₂), 3.00 (br m, 2H, CH₂ⁿPr), 1.66 (d, J = 6.0 Hz, 6H, CH(CH₃)₂), 1.63 (s, 18H, CH₃), 1.36 (s, 18H, CH₃), 1.15 (br m, 2H, CH₂ⁿPr), 0.36 (t, 3H, CH₃ⁿPr). ¹³C NMR (C₆D₆): δ 159.4, 142.6, 136.6, 124.2, 123.4, 122.5 (Ar), 88.8 (CH(CH₃)₂), 58.0 (CH₂CH₂N), 56.2 (ArCH₂), 35.1 (tBu Cq), 34.3 (Cq), 31.6 (tBu), 29.8 (tBu), 25.8 (CH(CH₃)₂), 14.0 (CH₂CH₂N), 11.3 (CH₃CH₂CH₂N). ⁵¹V NMR (C₆D₆): δ −514.

Ethylene polymerisation

Ethylene polymerisation reactions were performed in a flame-dried glass flask (250 mL) equipped with a magnetic stirrer bar. The flask was evacuated and filled with ethylene gas at 1 bar, which was maintained throughout the polymerisation. The flask was further purged several times with ethylene, and then 50 mL of dry, degassed toluene was added via a glass syringe. If applicable, the reactivating agent ETA was added (0.1 mL, 0.72 mmol) at this stage. The solution was then stirred for 10 min to allow ethylene saturation, and the correct temperature was acquired via the use of a water bath. The co-catalyst was added, and the solution was stirred for a further 5 min. The pro-catalyst was injected as a toluene solution (stock solutions of 1 μmol mol⁻¹ were prepared immediately prior to use). The polymerisation time was measured from pro-catalyst injection; the polymerisation was quenched by the injection of 5 mL of methanol. The resulting polymer was transferred into a 500 mL beaker containing acidified methanol, and the solid polyethylene was collected viafiltration and dried at 90 °C overnight.

Crystallographic studies

Crystals of 3 were obtained by cooling a toluene–pentane solution of 3, and its structure was determined. Crystal data collection and processing parameters are given in Table 1. The selected crystals, sensitive to air and moisture, were mounted on a glass fiber using perfluoropolyether oil and cooled rapidly to 180 K in a stream of cold N₂. Data collection were collected at low temperature (T = 180 K) on an Oxford Diffraction Kappa CCD Excalibur diffractometer, using a graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å) and equipped with an Oxford Cryosystems Cryostream Cooler Device. Final unit cell parameters were obtained by means of a least-squares refinement of a set of 8000 well measured reflections, and a crystal decay was monitored during data collection by measuring 200 reflections by image, no significant fluctuation of intensities has been observed. Structures have been solved by means of Direct Methods using the program SIR92,¹⁷ and subsequent difference Fourier maps, models were refined by least-squares procedures on a F² by using SHELXL-97¹⁸ integrated in the package WINGX version 1.64,¹⁹ and an empirical absorption corrections were applied on data.²⁰ Details of the structure solution and refinements are given in the Supporting Information (CIF file).†

Acknowledgements

We are grateful to the Centre National de la Recherche Scientifique (CNRS) and the University of East Anglia for financial support. Rapra Smithers Ltd are thanked for gpc measurements.

References

1. See for example: (a) V. Busico, Dalton Trans., 2009, 8794; (b) D. Takeuchi, Dalton Trans., 2010, 39, 311.
2. (a) J. W. M. Noordermeer, Ethylene-Propylene-Diene Rubber, in Kirk-Othmer Encyclopedia of Chemical Technology, ed. J. I. Kroschwitz, M. Howe-Grant and J. Wiley & Sons, New York, 4th edn, 1993, vol. 8, p. 978; (b) J. Mark, B. Erman and F. R. Eirich, “Science and Technology of Rubber”, Academic Press, London, 2nd edn, 1994; (c) W. Kaminsky and M. Arndt, in Applied Homogeneous Catalysis with Organometallic Compounds, ed. B. Cornils and W. A. Hermann, VCH, Weinheim, Germany, 1996, vol. 1, p. 230.
3. (a) S. Gambarotta, Coord. Chem. Rev., 2003, 237, 229; (b) H. Hagen, J. Boersma and G. van Koten, Chem. Soc. Rev., 2002, 31, 357.
4. For early examples see: (a) A. Gumboldt, J. Helberg and G. Schleitzer, Makromol. Chem., 1967, 101, 229; (b) D. L. Christman, J. Polym. Sci., Part A-1, 1972, 10, 471.
5. C. Redshaw, Dalton Trans., 2010, 39, 5595.
6. (a) K. Nomura and S. Zhang, Chem. Rev., 2011, 111, 2342; (b) C. Redshaw, Olefin Upgrading Catalysis by Nitrogen-based Metal Complexes I, ed. J. Cámpora and G. Giambastiani, Springer Science + Business Media B.V., 2011 DOI:10.1007/978-90-481-3815-9_4; (c) J.-Q. Wu and Y.-S. Li, Coord. Chem. Rev., 2011 DOI:10.1016/j.ccr2011.01.048 , In-press.
7. (a) W. Wang and K. Nomura, Adv. Synth. Catal., 2006, 348, 743; (b) Y. Onishi, S. Katao, M. Fujiki and K. Nomura, Organometallics, 2008, 27, 2590; (c) W. Zhang and K. Nomura, Inorg. Chem., 2008, 47, 6482; (d) M. C. W. Chan, K. C. Chen, C. I. Dalby, V. C. Gibson, A. Kohlmann, I. R. Little and W. Reed, Chem. Commun., 1998, 1673; (e) S. Scheuer, J. Fischer and J. Kress, Organometallics, 1995, 14, 2627; (f) C. Lorber, B. Donnadieu and R. Choukroun, J. Chem. Soc., Dalton Trans., 2000, 4497.
8. (a) Y. Nakayama, H. Bando, Y. Sonobe, Y. Suzuki and T. Fujita, Chem. Lett., 2003, 32, 766; (b) Y. Nakayama, H. Bando, Y. Sonobe and T. Fujita, Bull. Chem. Soc. Jpn., 2004, 77, 617; (c) Y. Nakayama, H. Bando, Y. Sonobe and T. Fujita, J. Mol. Catal. A: Chem., 2004, 213, 141; (d) D. M. Homden, C. Redshaw, J. K. A. Wright, D. L. Hughes and M. R. J. Elsegood, Inorg. Chem., 2008, 47, 5799; (e) J. Q. Wu, L. Pan, N. H. Hu and Y. S. Li, Organometallics, 2008, 27, 3840; (f) J. Houghton, S. Simonovic, A. C. Whitwood, R. E. Douthwaite, S. A. Carabineiro, J.-C. Yuan, M. M. Marques and P. T. Gomes, J. Organomet. Chem., 2008, 693, 717; (g) J. Q. Wu, L. Pan, S. R. Liu, L. P. He and Y. S. Li, J. Polym. Sci., Part A: Polym. Chem., 2009, 47, 3573.
9. L. M. Tang, J. Q. Wu, Y. Q. Duan, L. Pan, Y. G. Li and Y. S. Li, J. Polym. Sci., Part A: Polym. Chem., 2008, 46, 2038.
10. (a) S. Zhang, S. Katao, W.-H. Sun and K. Nomura, Organometallics, 2009, 28, 5925; (b) S. Zhang and K. Normura, J. Am. Chem. Soc., 2010, 132, 4960.
11. C. Redshaw, M. A. Rowan, D. M. Homden, S. H. Dale, M. R. J. Elsegood, S. Matsui and S. Matsuura, Chem. Commun., 2006, 3329.
12. C. Redshaw, M. A. Rowan, L. Warford, D. M. Homden, A. Arbaoui, M. R. J. Elsegood, S. H. Dale, T. Yamato, C. P. Casas, S. Matsui and S. Matsuura, Chem.–Eur. J., 2007, 13, 1090.
13. (a) C. Lorber, F. Wolff, R. Choukroun and L. Vendier, Eur. J. Inorg. Chem., 2005, 2850; (b) C. Lorber, Pure Appl. Chem., 2009, 81, 1205.
14. See for example: (a) G. Santoni, G. Licini and D. Rehder, Chem.–Eur. J., 2003, 9, 4700; (b) C. Wikete, P. Wu, G. Zampella, L. De Gioia, G. Licini and D. Rehder, Inorg. Chem., 2007, 46, 196.
15. E. Y. Tshuva, I. Goldberg, M. Kol and Z. Goldschmidt, Organometallics, 2001, 20, 3017 and references therein.
16. F. Wolff, C. Lorber, R. Choukroun and B. Donnadieu, Inorg. Chem., 2003, 42, 7839.
17. A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M. C. Burla, G. Polidori and M. Camalli, J. Appl. Cryst., 1994, 27, 435.
18. G. M. Sheldrick, in SHELX97 [Includes SHELXS97, SHELXL97, CIFTAB] - Programs for Crystal Structure Analysis (Release 97-2), Institüt für Anorganische Chemie der Universität, Tammanstrasse 4, D-3400 Göttingen, Germany, 1998.
19. L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837.
20. N. Walker and D. Stuart, Acta Crystallogr., Sect. A: Found. Crystallogr., 1983, 39, 158.

---

Footnote

† CCDC reference numbers 802723. For crystallographic data in CIF or other electronic format see DOI: 10.1039/c1cy00089f

---