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and ethylene polymerization/ring opening polymerization capability Jing Ma,a Ke-Qing Zhao,a Mark Walton,b Joseph A. Wright,b David L. Hughes,b Mark R.J. Elsegood,c Kenji Michiue,d Xinsen Sune and Carl Redshawa,e* 5

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Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX DOI: 10.1039/b000000x ABSTRACT：Reaction of the ligand 2,4-tert-butyl-6-[(2-methylquinolin-8-ylimino)methyl]phenol (L1H) with [VOCl3] in the presence of triethylamine afforded the complex [VOCl2L1] (1), whereas use of [VO(OnPr)3] led to the isolation of [VO2L1] (2) or [VO2L1]• 2/3MeCN (2•2/3MeCN). Reaction of 2-((2(1H-benzo[d]imidazol-2-yl)quinolin-8-ylimino)methyl)-4,6-R1,R2-phenols (R1 = R2 = tBu; L2H), (R1 = R2 = Me; L3H) or (R1 = Me, R2 = Ad; L4H) with [VO(OnPr)3] afforded complexes of the type [L2-4VO] (where L2 = 3, L3 = 4, L4 = 5). The molecular structures of 1 to 3 are reported; the metal centre adopts a distorted octahedral, trigonal bipyramidal or square-based pyramid, respectively. In Schlenk line tests, all complexes have been screened as pre-catalysts for the polymerization of ethylene using diethylaluminium chloride (DEAC) as co-catalyst in the presence of ethyltrichloroacetate (ETA), and for the ring opening polymerization (ROP) of ε-caprolactone in the presence of benzyl alcohol. All pre-catalyst/DEAC/ETA systems are highly active ethylene polymerization catalysts affording linear polyethylene with activities in the range 3,000 – 10,700 g/mol.h.bar; the use of methylaluminoxane (MAO) or modified MAO as cocatalyst led to poor or no activity. In a parallel pressure reactor, 3 – 5 have been screened as pre-catalysts for ethylene polymerization in the presence of either DEAC or DMAC (dimethylaluminium chloride) and ETA at various temperatures and for the co-polymerization of ethylene with propylene. The use of DMAC proved more promising with 3 achieving an activity of 63,000 g/mol.h.bar at 50 oC and affording UHMWPE (Mw ~ 2,000,000). In the case of the co-polymerization, the incorporation of propylene was 6.9 – 8.8 mol%, with 3 exhibiting the highest incorporation when using either DEAC or DMAC. In the case of the ring opening polymerization (ROP) of ε-caprolactone, systems employing complexes 1 - 5 were virtually inactive at temperatures < 110 °C; on increasing the Cl:V ratio at 110 °C, conversions of the order of 80 % were achievable.

were achievable.5 Meanwhile, in other studies, it has been noted that titanium complexes bearing the quinoline containing ligand 2,4-tert-butyl-6-[(2-methylquinolin-8-ylimino)methyl]phenol 1 The high activity and thermal stability exhibited by a number of (L H), were capable of both ethylene and propylene 45 polymerization, though the active species involved appeared not to 30 recent vanadium-based systems for olefin polymerization catalysis 6 has attracted both academic and industrial interest.1 This has also be simple. led to investigations into their potential use as catalysts for ring In general, the use of tridentate ligands sets has proved particularly opening polymerizations (ROP) of lactones and/or lactides.2 In our fruitful with group IV metals, as highlighted by the work of Tang et laboratory, vanadyl species bearing phenoxide-type ligand sets as al.,7 whilst Li and coworkers have investigated a number of 35 well as the use of imine-based ligand systems have been50 vanadium systems.8 Interestingly, the potentially tetra-dentate investigated, and some notable successes have been achieved.1c,3 In ligands L2H – L4H have previously been used to form more recent work, we found that by combining these two organoaluminium complexes, though they were shown by Sun et al functionalities in the form of bi-dentate phenoxyimines, similar to to be incapable of the ROP of ε-caprolactone under a variety of those employed in the Mitsui FI catalyst system,4 reasonably high conditions.9 40 activities for ethylene polymerization (≤ 10,000 g/mmol.h.bar) 55 Encouraged by these findings, we have prepared and fully a College of Chemistry and Materials Science, Sichuan Normal characterized a number of vanadyl complexes bearing tri- and tetraUniversity, Chengdu, 610066, China. dentate ligands (see scheme 1). Investigations into their ability to b School of Chemistry, University of East Anglia, Norwich, NR4 7TJ, UK polymerize ethylene revealed that, in the presence of the co-catalyst c Chemistry Department, Loughborough University, Leicestershire, LE11 diethylaluminium chloride (DEAC) and the re-activator 3TU, UK 10 60 ethyltrichloroacetate (ETA), activities of the order of 10,500 d Process Technology Center, Mitsui Chemicals Inc., 580-32 Nagaura, g/mol.h.bar were achievable. The operating temperature for Sodegaura, Chiba 299-0265, Japan. e optimum catalytic activity was found to be 60 °C; many previous Department of Chemistry, University of Hull, Hull, HU6 7RX, UK vanadium systems have suffered from thermal instability, primarily E-mail: [email protected] Fax: +44 1482 466410 Tel:+44 1482

Introduction

465219.

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Tri- and tetra-dentate imine vanadyl complexes: Synthesis, structure

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N N

N N

VOCl2 O

45

VO2 O

[VO 2L 1] (2)

[VOCl2L 1] (1)

50 N

N N

V O O

N

N

N N

V O O

N

N

N N

N

V O

O

Ad

[VOL2 ] (3)

[VOL3 ] (4)

Scheme 1

Results and Discussion 15

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[VOL4] (5)

. 60

Tri-dentate imine vanadyl complexes Reaction of 2,4-tert-butyl-6-[(2-methylquinolin-8ylimino)methyl]phenol (L1H) with [VOCl3] in the presence of triethylamine in tetrahydrofuran (THF) afforded, following workup (extraction into acetonitrile), the brown complex [VOCl2L1] (1) in 68 % isolated yield. Single crystals of the 1 were grown from a saturated acetonitrile solution at ambient temperature. The molecular structure is shown in Figure 1, with selected bond lengths and angles given in the caption; crystallographic data for 1 (and compounds 2, 2/ and 3) are collected in Table 4. In 1, the metal centre possesses a pseudo octahedral geometry with the tridentate ligand binding in mer fashion, and with the vanadyl group trans to the imino nitrogen. The V1 – N1 bond to the quinolone nitrogen is slightly longer than that to the ‘central’ nitrogen N2, which suggests that former forms a stronger bond; both V – N bonds are dative. The vanadyl bond length at 1.5911(14) Å is at the lower end of the range [1.593(2) – 1.605(4) Å] typically observed for this function.2c,3,11 65

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Figure 1. CAMERON representation of 1 showing the atom numbering scheme. Selected bond lengths (Å) and angles (°): V1 – O1 1.8105(14), V1 – O2 1.5911(14), V1 – N1 2.1669(17), V1 – N2 2.2090(16), V1 – Cl1 2.3610(6), V1 – Cl2 2.3147(6); O1 – V1 – N1 158.23(6), O2 – V1 – N2 173.64(7), Cl1 – V1 – Cl2 162.72(2). By contrast, interaction of L1H with [VO(OnPr)3] in refluxing toluene afforded, after work-up (extraction into acetonitrile), the yellow complex [VO2L1] (2) in 64 % isolated yield. Single crystals of 2 were grown from a saturated acetonitrile solution at ambient temperature. The molecular structure is shown in Figure 2, with selected bond lengths and angles given in the caption. There are three vanadium complexes and two molecules of acetonitrile in the asymmetric unit. The metal adopts a distorted trigonal bipyramidal geometry with the phenoxide oxygen and quinoline nitrogen atom occupying axial positions, and with cis oxo groups. The vanadyl bond lengths of 1.624(3) and 1.628(4) Å (and for 2/, see below, 1.629(2) and 1.623(2) Å) are longer than that observed in 1. Presumably the presence of the second oxo group arises via fortuitous hydrolysis, with two propoxide ligands of the vanadium precursor eliminated in the form of propanol. The mutual twist between the quinolinyl group and the C6H2 aromatic rings in 2 varies somewhat between the three unique complexes, viz 39.94(9) ° for that containing V1, 31.07(9) ° for V2 and 30.96(9) ° for V3, respectively. The molecules pack parallel to the b axis via π – π interactions (see ESI, Figure S1). The centroid – centroid separations are all close to 3.5 Å, with the closest atom – atom contacts at about 3.35 Å. There is a weak interaction C40 – H40 … O7/ between stacks at 2.43 Å.

Figure 2. CAMERON representation 2·2/3(MeCN) showing the atom numbering scheme. Selected bond lengths (Å) and angles (o): V1 – O1 1.913(3), V1 – O2 1.624(3), V1 – O3 1.628(4), V1 – N1 2.139(4), V1 – N2 2.164(4); O1 – V1 – N1 134.67(17), O2 – V1 – N2 98.21(15), O3 – V1 – N2 152.79(14). The reaction was repeated in an attempt to avoid the hydrolysis reaction; however, again, a dioxo complex was formed, which differed from 2 in the degree of solvation. This alternative crystalline form 2/ does not feature the stacking arrangement seen in 2 (see ESI, Figure S2 and geometrical parameters of 2/ and Table 4). Tetra-dentate imine vanadyl complexes Reaction of the ligands 2-((2-(1H-benzo[d]imidazol-2-yl)quinolin8-ylimino)methyl)-4,6-R1,R2-phenols (R1 = R2 = tBu; L2H), (R1 = R2 = Me; L3H) and (R1 = Me, R2 = Ad; L4H) with [VO(OnPr)3] in refluxing toluene afforded, after work-up (extraction into This journal is © The Royal Society of Chemistry [year]

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as a result of reduction to inactive species.11 The polymer products were mostly linear polyethylene of relatively high molecular weight35 (Mw) (≤ 32,400) at 30 °C, however the Mw values dropped rapidly on increasing the temperature. In contrast to the previous work on aluminium complexes,9 use of the ligands L2H – L4H herein provided vanadyl complexes which were shown to be capable of the ROP of ε-caprolactone with good control, albeit requiring the40 use of high temperatures (110 °C) to achieve reasonable conversions.

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acetonitrile), complexes of the type [L2-4VO] (R1 = R2 = tBu 3, R1 = R2 = Me 4, R1 = Me, R2 = Ad 5) in good yield (> 70 %). During the reaction, the vanadium centre was reduced from V(V) to V(IV), and we have attributed this to an oxidation reaction (of propanol) catalyzed by the vanadyl complex. Such reactions are well50 established for vanadyl complexes, including those bearing additional alkoxide ligands;12 mechanisms have been proposed.13 These vanadium(IV) complexes were characterized by X-band EPR measurements where possible at 298 K and, as expected, in the case of 3, gave an 8-line spectrum characteristic of V(IV) (d1, I = 7/2).55 Given the poor solubility of 4 and 5, the EPR spectra were recorded on solid samples only; g values compare favorably with previously reported vanadyl(IV) systems,14 and particularly with those adopting a VO[N2O2] coordination environment.3b,15 Crystals of 3.MeCN suitable for an X-ray structure determination60 were grown from a saturated solution in acetonitrile on prolonged standing (1 – 2 days) at ambient temperature. The molecular structure is shown in Figure 3, with selected bond lengths and angles given in the caption. The metal centre adopts a distorted square-based pyramid with the oxo group at the apex and the (L2)65 ligand wrapped around the four base sites. There is rotation about the C8 – N8 bond so that the normals to the phenolate ring of C11 – 16 and the quinoline system, N1 – C10, are ca 15 ° apart; the quinolone and benzimidazole ring systems are more coplanar with rotation about the C2 – C21 bond ca 1.7 ° from planarity.70 Molecules of 3 stack such that adjacent vanadyl groups align along the crystallographic a axis (see ESI, Figure S3) and the quinolinylbenzimidazole unit overlaps a centrosymmetrically-related unit with an inter-planar distance of ca. 3.35 Å.

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Over 15 min., at 30 °C and 1 bar ethylene, on changing the molar ratio of Al:V from 10,000 to 30,000 (runs 1 to 5), the highest activity was observed for Al:V at 20,000. Notably, the higher the Al:V ratio employed, the lower the molecular weight of the polyethylene obtained. At this temperature (30 °C), the products formed possessed relatively narrow molecular weight distributions (< 3). At an Al:V ratio of 20,000, the temperature was varied from 30 to 80 °C (runs 3 and 6 – 10), and the highest activity, namely 7,480 g/mmol.h.bar, was achieved at 60 °C. As observed in other vanadium-based systems, increasing the temperature led to a rapid decrease in the molecular weight of the product. 13C NMR spectral analysis of the polymers indicated that there was no branching present (see ESI, Figures S4 – S6); the lower melting points (≤ 128 °C) observed for some runs were thought to be due to the lower molecular weights of the products obtained as opposed to the presence of branching. Given the results in Table 1, the optimum conditions for screening of 1 – 5 were set at 60 °C and an Al:V ratio of 20,000; results under these conditions are presented in Table 2. For the tridentate systems (runs 1 and 2), the oxydichloride 1 exhibited superior activity, whereas for the dioxo complex 2, the molecular weight of the isolated polymer was somewhat greater; molecular weight distributions were similar for the two systems. In the case of the complexes bearing tetra-dentate ligand sets, complex 5 possessing the ortho adamantyl substituent exhibited the highest activity; this system also produced polyethylene possessing highest molecular weight. Comparison with the recently reported vanadyl complexes bearing bi-dentate phenoximine ligands reveals similar observed activities, molecular weights (Mw) and range of PDIs, although for the bidentate systems, the optimum operating temperature was found to be 80 °C.5

Parallel Pressure Reactor screening The effect of temperature on the pre-catalysts 3 – 5 in the presence of DMAC or DEAC and ETA was studied. The results are summarized in Table 3 and Figure 4; for ethylene uptake and plots of dwt/d(Log M) v Log Mw, see ESI, Figures S7 – S12 and S13 – S15, respectively (Fig. S16 compares the PDI values obtained using 85 3 – 5). In all cases, there was a dramatic fall off in observed activity on increasing the temperature from 50 to 140 oC. Indeed, only the systems employing complex 3 exhibited activity at temperatures in excess of 80 oC, with the system 3/DMAC/ETA exhibiting the highest activity (63,000 g/mol.h.bar at 50 oC) herein. For all 90 systems, ultra high molecular weight polyethylene (UHMWPE) was obtained at 50 oC (Mw ~ 1,000,000 to 2,200,000). As expected, on increasing the temperature, there was a rapid decrease in molecular weight (Mw) (~120,000 – 150,000 at 80 oC), whilst interestingly, the PDI values narrowed as the temperature increased. o 95 Melting points were in the range 126.7 – 135.9 C; the lower o melting points (≤ 130 C) observed for some runs were thought to Figure 3. CAMERON representation of 3·MeCN showing the atom be due to the inclusion of lower molecular weights of the products numbering scheme. Selected bond lengths (Å) and angles (o): V1 – obtained as opposed to the presence of branching. O1 1.589(3), V1 – O11 1.906(3), V1 – N1 2.036(3), V1 – N8 2.088(3), V1 – N22 2.071(4); O11 – V1 – N1 141.89(13), O11 – 100 Ethylene/propylene co-polymerization V1 – N8 87.89(13), N1 – V1 – N22 76.69(15). The co-polymerization of ethylene with propylene using 3 - 5 was conducted in the presence of either DMAC or DEAC and ETA at Catalytic screening 50 oC over 30 mins; results are presented in Table 4.The system employing 3/DMAC/ETA was found to exhibit the highest activity Ethylene polymerization 105 (7,400 g/mol.h.bar), whilst for 3 – 5, the use of DMAC resulted in Schlenk line tests: Complexes 1 - 5 were found to be active for the superior activities versus the use of DEAC as co-catalyst. Higher polymerization of ethylene using diethylaluminium chloride molecular weight products (Mw) were obtained when using DMAC (DEAC) as co-catalyst, with ethyltrichloroacetate (ETA) present as (vs DEAC) with the trend when using DMAC (5 > 4 > 3) being the re-activator. Complex 3 was used to obtain the optimum reverse of that observed for the catalytic activity (3 > 4 > 5). polymerization conditions and the results are presented in Table 1. 80

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Run

Al/V

T (℃)

T (min)

PE (g)

1 2 3 4 5 6 7 8 9 10 11

10000 15000 20000 25000 30000 20000 20000 20000 20000 20000 20000

30 30 30 30 30 40 50 60 70 80 60

15 15 15 15 15 15 15 15 15 15 30

0.0751 0.1038 0.1421 0.1335 0.0998 0.1594 0.1766 0.1871 0.1803 0.1612 0.2911

Activity (g/mmol.h.bar) 3000 4150 5680 5340 3990 6380 7060 7480 7210 6450 5820

Mw (x 103) 64.6 46.8 44.3 41.0 40.7 17.7 9.6 7.6 6.9 6.1 13.8

Mn (x 103) 32.4 17.0 19.7 18.2 13.9 3.8 2.4 2.2 1.9 1.9 2.5

PDI

Tm (°C)

1.99 2.75 2.25 2.25 2.93 4.68 4.09 3.52 3.68 3.18 5.54

134.10 133.49 133.26 133.12 132.52 130.13 128.00 126.79 126.71 127.46 128.05

20

Table 1. Polymerization screening using pre-catalyst 3.a

5

10

a Conditions: 0.1 µmol of [V] per run, 30 mL of toluene, 0.1ml ETA per run, 1 atm of ethylene. GPC analysis was conducted in 1,2,4- 25 trichlorobenzene.

For DEAC, the trend for Mw was 4 > 5 > 3, whilst that for the activity was 3 > 5 > 4. The PDIs for the DMAC runs were narrow30 (2.1 – 2.3) and even narrower for DEAC (~1.9). The trend for the %C3 incorporation (6.9 – 8.8 mol%) mirrored that of the catalytic activities. 35

40

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50

15

Figure 4. Activity in ethylene polymerization at 50 – 140 °C by 3 -55 5.

60

Ring opening polymerization The use of 1 - 5, in the presence of benzyl alcohol, for the ROP of ε-caprolactone was evaluated. The results are presented in Table 5; complex 1 was used to determine the conditions required for best results, and this revealed that only low conversions (< ca 22 %) were observed at temperatures below 90 °C. Increasing the temperature led to better conversions, which peaked at ca 81 % when using a CL:V ratio of 800 at 110 °C; further increasing the CL:V was detrimental. All systems were well behaved (good control) with PDI values generally less than 1.2, with the corrected average molecular mass16 of the polymers obtained close to the calculated values. Molecular weight of the products (Mw) isolated using complex 2 - 5 were remarkably consistent (~ 7,600 g mol-1), though conversion rates for these systems were disappointing (< 50 %). It should be noted however that the obtained PCL polymers exhibited much lower molecular weight than their calculated values Mn on the basis of the molar ratio of the monomer and Al cocatalyst, which may be attributed to chain transfer resulting from chain termination, suggesting a significant deviation from “living polymerization”. Within the family of complexes bearing tetradentate ligands, complex 5 bearing the adamantyl substituent exhibited highest conversion. We note that aluminium complexes bearing related tetra-dentate ligand sets were found to be poor initiators.9 In the MALDI-TOF spectra (see ESI, Figures S17 – S19), only one major population of peaks, which possess the spacing of 114 mass unit (the molecular weight of the monomer), was detected. The peaks are assigned to the sodium adducts of the polymer chains with benzyloxy end groups. A smaller series of peaks is associated with the use of protonated/sodiated (from the matrix) species from the matrix.17 The 1H NMR spectrum of the polymer was obtained (for example, see ESI, Figure S20) to verify the molecular weight of the polymer and identify the end chain group of the PCL. Typically, peaks at 7.29, 5.04 and 3.57 ppm (5:2:2) indicated that the polymer chains were capped by one benzyl ester and a hydroxyl group, consistent with insertion of a benzyloxy group during polymerization; 13C NMR data (ESI, Figure S21) also revealed peaks (δ 127.5, 127.2, 127.1 and 50.1) due to the benzyl group. The polymer molecular weight (Mn) was calculated from the ratio of the peaks at 5.12 and 4.06 ppm (see Table 3).

Table 2. Catalysis runs using pre-catalysts 1 - 5 under optimized conditions at 1 bar. Run

Complex

PE (g)

1

1

0.2173

4 | Journal Name, [year], [vol], 00–00

Activity (g/mmol.h.bar) 8690

Mw (x103) 7.6

Mn (x103) 2.5

PDI

Tm (°C)

3.03

127.91

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2 0.1410 5640 10.9 3.7 2.98 129.73 2 3 0.1871 7480 7.6 2.2 3.5 126.79 3 4 0.1362 5450 11.2 5.9 1.91 130.15 4 5 0.2673 10690 20.0 6.8 2.94 129.04 5 a Conditions: 0.1 µmol of [V] per run, 30 mL of toluene, 60 °C, 20,000 equivalents of Et2AlCl, 0.1 mL of ETA, 15 min, 1 atm of ethylene. GPC analysis was conducted in 1,2,4-trichlorobenzene. Table 3. Ethylene polymerization results for complexes 3 - 5a

a 5

T/ (°C) m/g

Act. by Act. by C2 uptake Act. by C2 uptake weight

b

(20 min)

b

(5 min)

b

Act. ratio

Mw

(20min/5 min) x10

3

Mn x10

3

PD I

1

3

DMAC

50

0.157

63.30

35.64

51.84

0.69

1910 575 3.3 135.2

2

3

DMAC

80

0.013

5.24

4.86

22.76

0.21

127

3

3

DMAC

110

0.000

0.00

0.00

0.00

-

-

-

-

4

3

DMAC

140

0.001

0.44

0.00

0.00

-

-

-

- 127.1

5

3

DEAC

50

0.041

16.36

13.52

21.81

0.62

6

3

DEAC

80

0.000

0.00

0.00

0.00

-

-

-

-

7

3

DEAC

110

0.0004

0.16

0.00

0.00

-

-

-

- 126.9

8

-

-

- 126.7

44.8 2.8 132.5 -

1210 199 6.1 133.7 -

3

DEAC

140

0.001

0.40

0.00

0.00

-

9

4

DMAC

50

0.010

3.84

3.83

22.89

0.17

10

4

DMAC

80

0.001

0.24

0.29

9.76

0.03

-

-

- 130.8

11

4

DMAC

110

0.000

0.00

0.00

0.00

-

-

-

-

-

12

4

DMAC

140

0.000

0.00

0.00

0.00

-

-

-

-

-

13

4

DEAC

50

0.003

1.04

1.82

14.88

0.12

-

-

- 133.4

14

4

DEAC

80

0.000

0.00

0.00

0.00

-

-

-

-

-

15

4

DEAC

110

0.000

0.00

0.00

0.00

-

-

-

-

-

16

4

DEAC

140

0.000

0.00

0.00

0.00

-

-

-

-

-

17

5

DMAC

50

0.073

29.08

15.24

21.01

0.73

2160 542 4.0 135.1

18

5

DMAC

80

0.018

7.16

5.54

15.49

0.36

150

19

5

DMAC

110

0.000

0.00

0.00

0.00

-

-

-

-

-

20

5

DMAC

140

0.000

0.00

0.00

0.00

-

-

-

-

-

21

5

DEAC

50

0.024

9.68

8.39

18.92

0.44

22

5

DEAC

80

0.000

0.00

0.00

0.00

-

-

-

-

-

23

5

DEAC

110

0.000

0.00

0.00

0.00

-

-

-

-

-

24

5

DEAC

140

0.000

0.00

0.00

0.00

-

-

-

-

-

2130 605 3.5 134.2

63.8 2.4 135.9

1020 197 5.2 134.5

Conditions: Runs conducted in toluene (5 ml) at over 30 min. All runs used 0.005 µmmol V, 0.8 MPa ethylene, 20,000 equivalents of ETA (v V) and

b 20,000 equivalents of co-catalyst (v V). Standard = VO(OEt)Cl2. Kg/mmolV.h. CDetermined by GPC, reported using polyethylene calibration.

Table 4. Co-polymerization results of ethylene/propylene for complexes 3 - 5a Run

Cat

Cat (µ µmol)

Co-cat

m/ g

Activity by weightb

Mw (x103)c

Mn (x103)c

PDI

%C3d

Tm

1

3

0.050

DMAC

0.185

7.39

156.9

67.6

2.32

8.8

78.6

2

3

0.050

DEAC

0.106

4.23

84.4

44

1.92

8.1

85.6

3

4

0.050

DMAC

0.145

5.82

216.6

103.6

2.09

7.8

80.6

4

4

0.050

DEAC

0.036

1.44

107.5

56.7

1.90

6.9

87.5

5

5

0.050

DMAC

0.061

2.43

289.5

136.7

2.12

7.1

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5

0.050

DEAC

0.052

2.06

104.7

55.8

1.87

7.1

86.9

Conditions: Runs conducted in toluene (5 ml) at 50 oC over 30 min. All runs used 0.005 µmmol V, 0.4 MPa ethylene, 0.4 MPa propylene, 2,000

b equivalents of ETA (v V) and 2,000 equivalents of co-catalyst (v V). Standard = VO(OEt)Cl2. Kg/mmolV.h. polyethylene calibration.

C

Determined by GPC, reported using

d Mol% determined by IR.

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In conclusion, a series vanadyl complexes bearing tri- or tetradentate ligand sets has been synthesized and characterized by 1H, 13 C, 51V NMR or EPR spectroscopy, elemental analysis, IR spectroscopy and where possible by single crystal X-ray diffraction. In the Schlenk line tests, complexes 1 – 5 exhibited high activity (ca. 5,500 – 10,700 g/mmol.h.bar) when using 20,000 equivalents of DEAC as co-catalyst in the presence of the re-activator ETA at 60 °C and 1 bar ethylene. The observed activity order was 5 > 1 > 3 > 2 ≈ 4. The products were moderate to high molecular weight (Mw), linear polyethylenes. In a parallel pressure reactor (PPR) using either DMAC or DEAC as cocatalyst in the presence of ETA, 3 – 5 were found to afford UHMWPE, whilst the observed activity order was 3 (tBu) > 5

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(Ad) >> 4 (Me). The difference between the observed activity trends for the Schlenk line tests and the PPR tests is thought to be due to the different conditions employed (eg the concentration of the co-catalyst employed). This highlights the need to be careful when comparing polymerization results conducted in different laboratories under even slightly different conditions. In the ROP of ε-caprolactone, moderate to good conversion was achieved at 110 °C, with molecular weights (Mw) in the range ~3,000 to 50,000 g mol-1; the systems were generally well-behaved with PDIs typically less than 1.2.

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Table 5. ε-Caprolactone screening results for complexes 1 - 5 a. Run Complex Ratio (CL:V) T (°C) Conversion b (%) Mw Mn GPC Mn NMR PDI 1 400 110 27.3 9704 6646 1.4 1 2 600 110 76.9 7558 6137 7734 1.2 1 3 800 110 81.3 6868 5788 5682 1.1 1 4 1000 110 26.4 6215 5560 1 5 800 90 21.9 7858 7025 1.1 1 6 800 70 9.9 8100 7085 1.1 1 7 800 50 0 1 8 800 110 10.7 7635 6817 7747 1.1 2 9 800 110 30.1 7518 6876 6151 1.1 3 10 800 110 24.2 7632 6923 11167 1.1 4 11 800 110 47.1 7672 6828 9685 1.1 5 a Conditions: 5 mL of toluene; 1 mL of ε-caprolactone; 1 equivalent of benzyl alcohol; 24 h. b Calculated by 1H NMR spectroscopy. GPC analysis was conducted in THF vs polystyrene standards. 35

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Synthesis of (E)-2-(2-methylquinolin-8-ylimino)-4,6-di-tertbutyl-phenolate oxovanadium dichloride (1) L1H (0.50 g, 1.34 mmol) was dissolved in tetrahydrofuran (40 mL). Triethylamine (0.20 mL, 1.44 mmol) and vanadium oxytrichloride (0.14 mL, 1.46 mmol) were added via syringe and the solution stirred at ambient temperature for 6 h. The volatiles were removed in vacuo. Crystallization using hot acetonitrile gave brown plates of the vanadium compound 1. (0.46 g, 68 % yield). MS (E.I.) 475.1 [M-Cl]+. IR (nujol): 1610m, 1588s, 1566m, 1538w, 1505m, 1431m, 1311m, 1232w, 1213m, 1199m, 1170m, 1146s, 972s, 886w, 796s, 764m, 694m. Found: C, 58.82; H, 5.87; N, 5.57. C25H29Cl2N2O2V requires C, 58.72; H, 5.72; N, 5.48 %. 1H NMR (CDCl3): 8.94 (s, 1H, CH=N), 8.24 (d, 1H, J = 8.40, ArH), 7.94 (d, 1H, J = 7.36, ArH), 7.81 (d, 1H, J = 7.84, ArH), 7.66 (d, 1H, J = 2.36, ArH) 7.61 (m, 2H, ArH) 7.48 (d, 1H, J = 2.36, ArH) 3.58 (s, 3H, Ar-Me), 1.63 (s, 9H, tBu), 1.38 (s, 9H, t Bu). 13C NMR (CDCl3) ： 161.0, 157.4, 152.7, 141.3, 138.9, 136.4, 130.7, 129.5, 128.6, 128.1, 127.1, 126.8, 126.1, 125.9, 115.3, 35.6, 35.1, 35.0, 30.9, 30.8, 30.1, 29.2, 28.7. 51V NMR (CDCl3): -261.47 (w1/2 = 256 Hz).

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Synthesis of (E)-2-(2-methylquinolin-8-ylimino)-4,6-di-tertbutyl-phenolate dioxovanadium(V) (2) L1H (0.50 g, 1.34 mmol) was dissolved in toluene (40 mL), and vanadyl tri-n-propoxide (0.34 mL, 1.46 mmol) was added via

Experimental General: All manipulations were carried out under an atmosphere of dry nitrogen using conventional Schlenk and cannula techniques or in a conventional nitrogen-filled glove box. Toluene was refluxed over sodium. Acetonitrile was refluxed over calcium hydride. All solvents were distilled and degassed prior to use. IR spectra (nujol mulls, KBr windows) were recorded on a Nicolet Avatar 360 FT IR spectrometer; 1H NMR spectra were recorded at room temperature on a Varian VXR 400 S spectrometer at 400 MHz or a Gemini 300 NMR spectrometer or a Bruker Avance DPX-300 spectrometer at 300 MHz. The 1H NMR spectra were calibrated against the residual protio impurity of the deuterated solvent. EPR spectra were recorded on a JESFA200 spectrometer at Tsinghua University. Elemental analyses were performed by the elemental analysis service at the London Metropolitan University. Magnetic moments were measured on a Johnson Matthey magnetic susceptibility balance. The ligands L13 H were prepared as described in the literature.6,9 The vanadium precursors were purchased from Sigma Aldrich and were used as received.

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syringe and the solution refluxed for 16 h. The solution was allowed to cool to room temperature and the volatiles were removed in vacuo. Crystallization using hot acetonitrile gave yellow needles of the vanadium compound 2. (0.39 g, 64 % yield). MS (E.I.) 456.1 [M]+, 441.0 [M-Me]+. IR (nujol): 1613s, 1587s, 1556m, 1538s, 1508m, 1323m, 1253s, 1200m, 1181s, 1171s, 1149m, 1134w, 987w, 969w, 942s, 895w, 843s, 792s, 754m. Found: C, 65.63; H, 6.46; N, 6.23. C25H29N2O3V requires C, 65.78; H, 6.40; N, 6.14 %. 1H NMR (CDCl3): 9.17 (s, 1H, CH=N), 8.30 (d, 1H, J = 8.35, ArH), 7.93 (d, 1H, J = 7.60, ArH), 7.81 (d, 1H, J = 7.95, ArH), 7.68 (ABq, 2H, ∆vAB = 5.72, J = 6.70, ArH) 7.60 (d, 1H, J = 8.35, ArH) 7.36 (d, 1H, J = 2.40, ArH), 3.82 (s, 3H, Ar-Me), 1.50 (s, 9H, tBu), 1.36 (s, 9H, tBu). 13 C NMR (CDCl3): 166.3, 165.7, 163.5, 144.2, 140.9, 140.8, 140.4, 138.9, 134.0, 128.2, 127.6, 127.4, 126.2, 120.8, 115.6, 35.5, 34.3, 31.3, 29.6, 27.5. 51V NMR (CDCl3): -535.93 (w1/2 = 535). Synthesis of 2-((2-(1H-benzo[d]imidazol-2-yl)quinolin-8ylimino)methyl)-4,6-di-tert-butyl-phenolate oxovanadium(IV) (3) L2H (0.80 g, 1.68 mmol) was dissolved in toluene (40 mL), and vanadyl tri-n-propoxide (0.41 mL, 1.8 mmol) was added via syringe and the solution refluxed for 16 h. The solution was allowed to cool to room temperature and the volatiles were removed in vacuo. Crystallization from hot acetonitrile gave yellow needles of the vanadium compound 3 (0.73 g, 79 % yield). MS (E.I.) 541 [M]+. IR (Nujol): 1600m, 1585w, 1529w, 1261m, 1094s, 1020s, 865w, 800s, 749w, 737w. Found: C, 68.68; H, 5.57.; N, 10.19, C31H31N4O2V requires C, 68.75; H, 5.58; N, 10.34. EPR (toluene, 298K): giso = 1.99, Aiso = 90 G.

Synthesis of 2-((2-(1H-benzo[d]imidazol-2-yl)quinolin-8ylimino)methyl)-4,6-dimethyl-phenolate oxovanadium(IV) (4)

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L H (0.17 g, 0.43 mmol) was dissolved in toluene (20 mL), and vanadyl tri-n-propoxide (0.11 mL, 0.44 mmol) was added via syringe and the solution refluxed for 16 h. The solution was allowed to cool to room temperature and the volatiles were removed in vacuo. Crystallization from either acetonitrile or dichloromethane gave yellow needles of the vanadium compound 4 (0.15 g, 76 % yield). MS (E.I.) 457 [M]+. IR: 1606m, 1587m, 1547m, 1516w, 1425w, 1374m, 1322w, 1301m, 1258s, 1218m, 1012s, 980s, 861m, 794s, 748s. Found: C, 41.8; H, 3.5; N, 6.8 %. C25H18N4O2V•4½CH2Cl2 requires C, 41.9; H, 3.2; N, 6.6. EPR (solid, 298K): giso = 2.00

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Synthesis of 2-((2-(1H-benzo[d]imidazol-2-yl)quinolin-8ylimino)methyl)-4-methyl,6-adamantyl-phenolate oxovanadium(IV) (5) L4H (0.10 g, 0.19 mmol) was dissolved in toluene (20 mL), and vanadyl tri-n-propoxide (0.05 mL, 0.21 mmol) was added via syringe and the solution refluxed for 16 h. The solution was allowed to cool to room temperature and the volatiles were removed in vacuo. Crystallization from hot acetonitrile or dichloromethane gave brown needles of the vanadium compound 5 (0.06 g, 55 % yield). MS (E.I.) 577.17 [M]+. IR: 1643w, 1610s, 1540s, 1445w, 1406m, 1338m, 1294s, 1226s, 1166m, 1093w, 1040m, 1018m, 957s, 839s, 767m, 709w, 676m. Found: C, 57.86; H, 4.47; N, 7.49 %. C34H30N4O2V•1½CH2Cl2 requires C, 57.91; H, 4.26; N, 7.95 %. EPR (solid, 298K): giso = 1.98.

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Ethylene polymerization (Schlenk line screening, Tables 1 and 2) Ethylene polymerisation reactions were performed in a dried Schlenk glass flask (250 mL) equipped with a magnetic stirrer bar. The flask was evacuated and recharged 3 times with ethylene, and then 20 mL of dry, degassed toluene was added via a glass syringe. The solution was then stirred for 10 min to allow ethylene saturation, and the correct temperature was acquired using an oil bath. The co-catalyst and the reactivating agent ETA were added (0.1 mL, 0.72 mmol); 10ml toluene, which dissolved the complex, was also added. The polymerisation time was measured from pre-catalyst injection; the polymerisation was quenched by the injection of 5 mL of ethanol. The resulting polymer was transferred into a 500 mL beaker containing acidified ethanol, and the polyethylene was collected by filtration and dried at 50 °C under vacuum overnight. Typical Parallel Pressure Reactor Polymerization Run (Tables 3 and 4) Polymerization reactions were performed in a parallel pressure reactor (Argonaut Endeavor® Catalyst Screening System) containing 8 reaction vessels (15 mL) each equipped with a mechanical stirrer and monomer feed lines. At first, a toluene solution (and a toluene solution of ETA as necessary) was injected into each vessel. For ethylene polymerization, the solution was heated to the polymerization temperature (Tp ) and thermally equilibrated, and the nitrogen atmosphere was replaced with ethylene and the solution was saturated with ethylene at the polymerization pressure. For ethylene/propylene copolymerization, the nitrogen atmosphere was replaced with propylene and the reaction vessels were pressurized with propylene (0.4 MPa at 25 oC), and the solution was heated to the Tp and thermally equilibrated, then ethylene was introduced into the reactor up to the polymerization pressure. In all cases the polymerization was started by addition of a toluene solution of alkyl aluminum or alkyl aluminium chloride followed by addition of a toluene solution of the vanadium complex (0.50 mL toluene solution of complex followed by 0.25 mL toluene wash). The total volume of the reaction mixture was 5 mL for all polymerizations. The pressure was kept constant by feeding ethylene on demand. After the reaction, the polymerization was stopped by addition of excess isobutyl alcohol. The resulting mixture was added to acidified methanol (45 ml containing 0.5 ml of concentrated HCl). The polymer was recovered by filtration, washed with methanol (2 × 10 ml) and dried in a vacuum oven at o 80 C for 10 h. Polymer Characterization (Tables 3 and 4) The melt transition temperatures (Tm) of the polyethylene (PE) and ethylene/propylene copolymer (EPR) were determined by differential scanning calorimetry (DSC) with a Shimadzu DSC60 instrument. The polymer samples were heated at 50 oC/min from 20 oC to 200 oC, held at 200 oC for 5 min, and cooled to 0 o C at 20 oC/min. The samples were held at this temperature for 5 min, and then reheated to 200 oC at 10 oC/min. The reported Tm was determined from the second heating scan unless otherwise noted. Molecular weights (Mw and Mn) and polymer disparity index (PDI) of PE and EPR were determined using a Waters GPC2000 gel permeation chromatograph equipped with four TSKgel columns (two sets of TSKgelGMH6-HT and two sets of TSKgelGMH6-HTL) at 140 oC using polystyrene calibration. oDichlorobenzene (ODCB) was used as the solvent. The propylene content of the EPR was measured by IR analysis using a JASCO FT-IR.18 Journal Name, [year], [vol], 00–00 | 7

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Crystallography Intensity data were collected on a Rigaku R-AXIS Rapid IP diffractometer (1), a Rigaku Saturn724+ with a rotating anode Xray source (2), an Oxford Diffraction Xcalibur-3/Sapphire3-CCD (2’), or a Bruker SMART 1000 CCD diffractometer using narrow slice 0.3° ω-scans (3). All data were measured with monochromated Mo-Kα radiation. Structures were determined by the direct methods routines in SHELXS-9719 or Superflip,20 and were refined by full-matrix least-squares methods on F2 in

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Acknowledgements

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We thank Sichuan Normal University for financial support. The EPSRC X-ray service at Southampton is thanked for the data collection for complex 2.

Supporting Information Available: X-ray crystallographic files, in CIF format, from the structure determinations of compounds 1 – 3. Stacking diagrams for complexes 2 and 3, and CAMERON representation of 2/. Selected spectra (1H, 13C NMR and MALDI TOF of polymer samples); Ethylene uptake for 3 -5 and plots of dwt/d(Log M) v Log Mw.

Table 6. Crystallographic data for complexes 1, 2·2/3(MeCN), 2’ and 3·MeCN. Compound

1

Formula

C25H29Cl2N2O2V

Formula weight Crystal system Space group a (Å) b (Å) c (Å) α (º) β (º) γ (º) V (Å3) Z Temperature (K) Wavelength (Å) Calculated density (g.cm-3) Absorption coefficient (mm-1) Transmission factors (min./max.) Crystal size (mm) θ(max) (°) Reflections measured Unique reflections Rint Reflections with F2 > 2σ(F2) Number of parameters R1 [F2 > 2σ(F2)] wR2 (all data) GOOF, S Largest difference peak and hole (e Å–3)

511.34 Triclinic P1 8.9979(4) 12.6300(6) 13.0073(9) 61.214(4) 78.851(6) 70.715(5) 1221.78(12) 2 100(2) 0.71075 1.390 0.649 0.872 and 1.000 0.10 × 0.40 × 0.01 27.47 16140 5555 0.0385 5555 296 0.0389 0.0966 1.062

2 C25H29N2O3V— 0.67(C2H3N) 483.81 Monoclinic P21/n 26.127(17) 10.845(8) 26.44(2) 90 91.646(12) 90 7489(9) 12 100(2) 0.71073 1.287 0.428 0.931 and 0.996 0.17 × 0.05 × 0.01 31.48 60185 22162 0.0892 15014 1265 0.1250 0.1893 1.194

456.44 Monoclinic P21/c 11.9806(4) 10.2865(4) 17.9031(12) 90 98.769(7) 90 2180.56(18) 4 100(2) 0.71075 1.390 0.485 0.718 and 1.000 0.10 × 0.40 × 0.01 27.48 15333 4999 0.0353 4998 287 0.0535 0.1586 1.075

3·MeCN C31H30N4O2V —C2H3N 582.58 Monoclinic P21/c 11.8130(4) 14.8706(4) 17.5707(7) 90 103.120(3) 90 3006.01(18) 4 140(1) 0.71073 1.287 0.368 0.981 and 1.022 0.15 x 0.14 x 0.02 21.3 36680 3330 0.154 2217 371 0.056 0.084 1.017

0.718 and –0.488

0.508 and –0.839

0.567 and -1.175

0.26 and -0.25

2’ C25H29N2O3V

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References 55

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See for example (a) Y. Onishi, S. Katao, M. Fujiki and K. Nomura, Organometallics, 2008, 27, 2590. (b) J. Q. Wu, L. Pan, N. H. Hu and Y. S. Li, Organometallics, 2008, 27, 3840. (c) C. Redshaw, Dalton Trans., 2010, 39,

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ε-Caprolactone procedure Typical polymerization procedures in the presence of one equivalent of benzyl alcohol (Table 3, run 1) were as follows. A toluene solution of 3 (0.025 mmol, 1.0 mL toluene) and BnOH (0.025 mmol) were added into a Schlenk tube in the glove-box at room temperature. The solution was stirred for 2 min, and then εcaprolactone (2.5 mmol) along with 1.5 mL toluene was added to the solution. The reaction mixture was then placed into an oil bath pre-heated at 110 °C, and the solution was stirred for the prescribed time (24 h). The polymerization mixture was then quenched by addition of an excess of glacial acetic acid (0.2 mL) into the solution, and the resultant solution was then poured into methanol (200 mL). The resultant polymer was then collected on filter paper and was dried in vacuo.

SHELXL-97 or SHELXL-2013.21 Non-hydrogen atoms were refined with anisotropic thermal parameters. Hydrogen atoms were included in idealized positions and their Uiso values were set to ride on the Ueq values of the parent carbon atoms except for 2 where H atoms were freely refined. Crystal data and refinement results for all samples are collated in Table 4. CCDC 998655-998658 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

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5595 and references therein. (d) D. Wang, Z. Zhao, T.B. Mikenas, X. Lang, L.G. Echevskaya, C. Zhao,

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J.A. Wright and M.R.J. Elsegood, Dalton Trans., 2009, 8911. (c) L. Clowes, M. Walton, C. Redshaw, Y. Chao, A. Walton, P. Elo, V. Sumerin and D.L. Hughes, Cat, Sci & Technol., 2013, 3, 152. D.M. Homden, C. Redshaw and D.L. Hughes, Inorg. Chem., 2007, 46, 10827. (b) D.M. Homden, C. Redshaw, J.A. Wright, D.L. Hughes and M.R.J. Elsegood, Inorg. Chem., 2008, 47, 5799. For a comprehensive review of metal pre-catalysts for olefin polymerization bearing phenoxyimines see H. Makio, H. Terao, A. Iwashita and T. Fujita, Chem. Rev., 2011, 111, 2363. J. Ma, K.-Q. Zhao, M. Walton, J. A. Wright, J. W.A. Frese, M.R.J. Elsegood, Q. Xing, W.-H. Sun and C. Redshaw, Dalton Trans., 2014, 43, 8300. G. Paolucci, A. Zanella, L. Sperni, V. Bertolasi, M. Mazzeo, C. Pellecchia, J. Mol. Cat., 2006, 258, 275. C. Redshaw and Y. Tang, Chem. Soc. Rev., 2012, 41, 4484. J.Q. Wu and Y.-S. Li, Coord. Chem. Rev., 2011, 255, 2303. M.Shen, W. Shang, K. Nomura and W.-H. Sun, Dalton Trans., 2009, 9000. For early use of ETA see (a) A. Gumboldt, J. Helberg, and G. Schleitzer, Makromol. Chem., 1967, 101, 229. (b) D.L. Christman, J. Polym. Sci. Part A-Polym. Chem., 1972, 10, 471. (c) E. Addison, A. Deffieux, M. Fontanille and K.J. Bujadoux, Polym. Sci., Part A, 1994, 32, 1033. D.M. Homden, C. Redshaw, L. Warford, D.L. Hughes, J.A. Wright, S.H. Dale and M.R.J. Elsegood, Dalton Trans., 2009,8900. See for example, (a) Y. Maeda, N. Kakiuchi, S. Matsumura, T. Nishimura, T. Kawamura and S. Uemura, J. Org. Chem. 2002, 67, 6718. (b) S.K. Hanson, R. Wu and L.A. Silks, Org. Lett., 2011, 13, 1908. (c) G. Zhang, B.L. Scott, R. Wu, L.A. Silks and S.K. Hanson, Inorg. Chem., 2012, 51, 7354. (a) S. Velusmany and T. Punniyamurthy, Org. Lett., 2004, 6, 217. (b) S.K. Hanson, R.T. Baker, J.C. Gordon, B.L. Scott, L.A. Silks and D.L. Thorn, J. Am. Chem. Soc., 2010, 132, 17804. (a) J. Slebin, Chem. Rev. 1965, 65, 153. (b) J. Costa Pessoa, M.J. Calhorda, I. Correia, M.T. Duarte and V. Felix, J. Chem. Soc. Dalton Trans., 2002, 4407. H. Yue, D. Zhang, Z. Shi and S. Feng, Solid State Sci., 2006, 8, 1368. T. Biela, A.Duda and S. Penczek, Macromol. Symp., 2002, 183, 1. N. Ikpo, C. Hoffmann, L.N. Dawe and F.M. Kerton, Dalton Trans. 2012, 41, 6651. C. Tosi and T. Simonazzi, Angew. Makromol. Chem. 1973, 32, 153. SMART (2001) and SAINT (2001), software for CCD diffractometers. Bruker AXS Inc., Madison, USA.G.M. Sheldrick, SHELXTL user manual, version 6.10. Bruker

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M.A.Matsko and W. Wu, Polym. Chem., 2012, 3, 2377. (e) Q. Yan, Z. Sun, W. Zhang, K. Nomura and W.-H. Sun, Macromol. Chem. Phys. 2014, doi:10.1002/macp.201400199 (a) J. Yamada and K. Nomura, Organometallics, 2005, 24, 3621. (b) A. Arbaoui, C. Redshaw, D.M. Homden,

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A number of vanadyl complexes bearing tri- or tetra-dentate phenoxyimine ligands have been structurally characterized and shown to exhibit high catalytic activity for ethylene polymerization in the presence of diethylaluminum chloride and ethyltrichloroacetate; at high temperatures, such complexes were also capable of the ROP of ε-caprolactone.

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Graphical Abstract