Next Article in Journal / Special Issue
Half-Titanocenes Containing Anionic Ancillary Donor Ligands: Effective Catalyst Precursors for Ethylene/Styrene Copolymerization
Previous Article in Journal / Special Issue
Precise Active Site Analysis for TiCl3/MgCl2 Ziegler-Natta Model Catalyst Based on Fractionation and Statistical Methods

Catalysts 2013, 3(1), 148-156; https://doi.org/10.3390/catal3010148

Article
Ethylene Polymerization Using (Imino)vanadium(V) Dichloride Complexes Containing (Anilido)methyl-pyridine, -quinoline Ligands–Halogenated Al Alkyls Catalyst Systems
1
Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan
2
Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100190, China
*
Author to whom correspondence should be addressed.
Received: 25 December 2012; in revised form: 29 January 2013 / Accepted: 30 January 2013 / Published: 7 February 2013

Abstract

:
The effect of ligand and Al cocatalysts in ethylene polymerization, using V(N-1-adamantyl)Cl2(L) [L = 2-(2,6-Me2C6H3)NCH2(C9H6N), 8-(2,6-Me2C6H3)NCH2(C9H6N)] and V(N-2-MeC6H3)Cl2[2-(2,6-R'2C6H3)NCH2(C5H4N)] (R' = Me, iPr), has been explored. The reaction products in the presence of Et2AlCl or Me2AlCl cocatalyst were polyethylene whereas the reaction product of the 2-methylphenylimido analogues in the presence of MAO cocatalyst was 1-butene with high selectivity, suggesting that the catalyst/cocatalyst nuclearity effect plays a role in this catalysis.
Keywords:
ethylene; vanadium catalysts; polymerization; ligand effect

1. Introduction

Designing vanadium complex catalysts for olefin polymerization/oligomerization has been considered as a promising subjects, because the classical Ziegler-type catalyst systems [V(acac)3, VOCl3, etc. and Et2AlCl, EtAlCl2, nBuLi, etc.] display unique high reactivity toward olefins in olefin coordination/insertion polymerization [1,2,3,4,5]. We previously reported that (arylimido)vanadium(V) complexes, containing anionic donor ligands (L), V(N-2,6-Me2C6H3)Cl2(L) (L = aryloxo, ketimide, phenoxyimine etc.), exhibited remarkable catalytic activities for ethylene polymerization in the presence of Al cocatalysts [3,4,5,6,7,8,9,10]. The activity by the aryloxo analogue was strongly affected by the Al cocatalyst; the activities in the presence of halogenated Al alkyls (iBu2AlCl, EtAlCl2, Me2AlCl, Et2AlCl) were higher than those in the presence of methylaluminoxane (MAO) [7,8]. Both the activity, and the norbornene incorporation, in the ethylene/norbornene copolymerization were also affected by the Al cocatalyst employed [7,8]. We thus speculated that a reason for the observed difference would be due to a formation of the different catalytically-active species, catalyst/cocatalyst nuclearity effect (assumed in Scheme 1) [5,11,12,13]. The activity decreased upon addition of CCl3CO2Et (for example, [14]), which can be commonly used as effective additives to improve the catalyst stability [8], clearly suggesting that the active species were, thus, different from those prepared from vanadium(III), (IV) complexes [1,2,3,4,5,14].
Scheme 1. Proposed catalytically-active species formed by different Al cocatalysts.
Scheme 1. Proposed catalytically-active species formed by different Al cocatalysts.
Catalysts 03 00148 g002
More recently, we demonstrated that the (adamantylimido)vanadium(V) complexes containing (2-anilidomethyl)pyridine ligand, V(NAd)Cl2[2-ArNCH2(C5H4N)] [Ad = 1-adamantyl; Ar = 2,6-Me2C6H3 (1a), 2,6-iPr2C6H3 (1b)], efficiently dimerize ethylene with both notable catalytic activities, and high selectivity in the presence of MAO [15,16], whereas the reaction products by 1a,b in the presence of Me2AlCl or Et2AlCl cocatalyst were ultrahigh molecular weight polyethylene (PE) (runs 1–5, Table 1) [16]. Moreover, we prepared the adamantylimido complexes containing 2- or 8-(anilidomethyl)-quinoline ligands, V(NAd)Cl2[(2,6-Me2C6H3)NCH2(C9H6N)] (2a,3a, Scheme 2), and V(N-2-MeC6H4)Cl2[2-ArNCH2(C5H4N)] complexes (4a,b) and explored reactions with ethylene in the presence of MAO (Table 1) [17]: remarkable effect of the imido ligand toward the selectivity (oligomer, polymer) was observed in the presence of MAO (Table 1, runs 9–12), whereas the reaction products by the quinoline analogues were a mixture of PE and oligomers. Since the reaction products by 1a,b in presence of Et2AlCl or Me2AlCl were PE, in this paper, we thus explored reactions with ethylene in the presence of halogenated Al alkyls to confirm our hypothesis outlined in Scheme 1, for example in ethylene polymerization by the other vanadium complex catalysts, [18,19,20,21,22,23,24].
Table 1. Reaction of ethylene with V(NR)Cl2(L) [R = Ad, L = 2-(2,6-R'2C6H3)NCH2(C5H4N) [R' = Me (1a), iPr (1b)], 2-(2,6-Me2C6H3)NCH2(C9H6N) (2a), 8-(2,6-Me2C6H3)NCH2(C9H6N) (3a); R = 2-MeC6H4 (4a,b), 2,6-Me2C6H3 (5a,b), L = 2-(2,6-R'2C6H3)NCH2(C5H4N)]–MAO or R''2AlCl (R'' = Me, Et) catalysts a.
Table 1. Reaction of ethylene with V(NR)Cl2(L) [R = Ad, L = 2-(2,6-R'2C6H3)NCH2(C5H4N) [R' = Me (1a), iPr (1b)], 2-(2,6-Me2C6H3)NCH2(C9H6N) (2a), 8-(2,6-Me2C6H3)NCH2(C9H6N) (3a); R = 2-MeC6H4 (4a,b), 2,6-Me2C6H3 (5a,b), L = 2-(2,6-R'2C6H3)NCH2(C5H4N)]–MAO or R''2AlCl (R'' = Me, Et) catalysts a.
RunV complex Al cocat.Al/V bC4',C6'Polyethylene (PE)
(μmol) Activity cC4'/% dC6'/% dActivity eMw fMw/Mn f
11a (0.2) gMAO5005780096.83.2
21a (0.1) gMAO15007650097.03.0
31b (0.5) gMAO10003570092.17.9
41a (5.0) hEt2AlCl100 1375.92 i
51a (5.0) hMe2AlCl200 7046.76 i
62a (5.0) jMAO10004371.628.453
73a (2.0) jMAO100020192.47.630
83a (2.0) jMAO150024992845
94a (0.2) jMAO6005030095.24.8
104b (0.2) jMAO7004150097.12.9
115a (2.0) kMAO3000 782.982.0
125b (2.0) kMAO3000 1892.932.6
a Conditions: toluene 30 mL, ethylene 8 atm., 25 °C, 10 min MAO or R"2AlCl (R" = Me, Et). b Al/V molar ratio. c Activity in (kg of ethylene reacted)/mol-V·h. d Determined by GC analysis. e Activity in kg-PE/mol-V·h. fGPC data in O-dichlorobenzene versus polystyrene standards. g Data cited from reference [15]. h Data cited from reference [16] and 0 °C. iMν value measured by viscosity. j Data cited from reference [17]. k Data cited from reference [10].
Scheme 2. List of complexes employed in this study.
Scheme 2. List of complexes employed in this study.
Catalysts 03 00148 g003

2. Results and Discussion

2.1. Ethylene Polymerization Using V(NAd)Cl2[2-ArNCH2(C9H6N)], V(NAd)Cl2[8-ArNCH2(C9H6N)]–Me2AlCl Catalyst Systems

Reactions of ethylene with V(NAd)Cl2[2-(2,6-Me2C6H3)NCH2(C9H6N)] (2a), V(NAd)Cl2[8-(2,6-Me2C6H3)NCH2(C9H6N)] (3a) in the presence of Me2AlCl were conducted in toluene and the results are summarized in Table 2. The results with V(NAd)Cl2[2-(2,6-Me2C6H3)NCH2(C5H4N)] (1a) [16], are also shown for comparison. Me2AlCl was chosen, because Me2AlCl showed higher catalytic activity than Et2AlCl in ethylene polymerization using 1a,b [16].
It turned out that the quinoline analogues 2a,3a showed the higher catalytic activities than the pyridine analogue (1a) especially under the optimized Al/V molar ratios: the activities were affected by the Al/V molar ratios. The reaction products were polyethylene that are insoluble in hot O-dichlorobenzene for measurement of their molecular weight(s) by GPC in the ordinary analysis procedure, suggesting formations of ultrahigh molecular weight polymers as observed previously [8,16,17]. The activity by 2a showed higher than 3a, probably due to a stability of catalytically active species (formed five membered ring around vanadium and L in 2a vs. six membered ring in 3a). The facts observed should be promising, because the reaction products were a mixture of PE and 1-butene (major) when the reactions by 2a,3a were conducted in the presence of MAO. Moreover, the observed activities in the presence of Me2AlCl were higher than those in the presence of MAO.
Table 2. Ethylene polymerization with V(NAd)Cl2(L) [L = 2-ArNCH2(C5H4N) (1a), 2-ArNCH2(C9H6N) (2a), 8-ArNCH2(C9H6N) (3a), Ar = 2,6-Me2C6H3]–Me2AlCl catalysts a.
Table 2. Ethylene polymerization with V(NAd)Cl2(L) [L = 2-ArNCH2(C5H4N) (1a), 2-ArNCH2(C9H6N) (2a), 8-ArNCH2(C9H6N) (3a), Ar = 2,6-Me2C6H3]–Me2AlCl catalysts a.
RunVanadium complexAl/V bYieldActivity c
L (V cat.)/μmol /mg
5 d2-ArNCH2(C5H4N) (1a) e0.520058.7704
13 d2-ArNCH2(C5H4N) (1a) f1.0500116696
142-ArNCH2(C9H6N) (2a)0.2250070.22110
152-ArNCH2(C9H6N) (2a)0.250001223670
162-ArNCH2(C9H6N) (2a)0.275001524560
172-ArNCH2(C9H6N) (2a)0.2100001203600
188-ArNCH2(C9H6N) (3a)0.2100079.62390
198-ArNCH2(C9H6N) (3a)0.2200073.62210
208-ArNCH2(C9H6N) (3a)0.2500058.71760
a Conditions: toluene 30 mL, ethylene 8 atm, 0 °C, 10 min. b Molar ratio of Al/V. c Activity in kg-PE/mol-V·h.; d Data cited from reference [16]. e Mν = 6.76×106 measured by viscosity. f Mν = 8.96×106 measured by viscosity.

2.2. Ethylene Polymerization Using V(N-2-MeC6H4)Cl2[2-(2,6-R'2C6H3)NCH2(C5H4N)]–Halogenated Al Alkyls Catalyst Systems

We recently reported [17] that the 2-methylphenylimido analogues, V(N-2-MeC6H4)Cl2[2-(2,6-R2C6H3)NCH2(C5H4N)] [R' = Me (4a), iPr (4b)], exhibited remarkable catalytic activities for ethylene dimerization in the presence of MAO [17], whereas the reaction by 2,6-dimethylphenylimido analogues (5a,b) afforded polyethylene (Table 1, runs 11–12) [10]. Since the reaction product by the adamantylimido analogues (1a,b) in the presence of halogenated Al alkyls (in place of MAO) afforded ultrahigh molecular weight polyethylene, we thus conducted the reaction with ethylene in the presence of Et2AlCl, Me2AlCl (Table 2). The results by the 2,6-dimethylphenylimido analogues (5a,b) [10] are also shown for comparison.
Although reaction with ethylene by 4a,b afforded 1-butene exclusively in the presence of MAO, and the activities are similar to those by 1a,b, the activities by 4a,b in the presence of Me2AlCl, Et2AlCl were low in all cases. The reaction products were polyethylene that were insoluble in hot O-dichlorobenzene for measurement of their molecular weight(s) by GPC in the ordinary analysis procedure, suggesting formations of ultrahigh molecular weight polymers [8,16,17]. The activities were affected by the Al/V molar ratios employed, but the activities by 4a showed higher than those by 4b [ex. activity: 382 kg-PE/mol-V·h by 4a (run 25) vs. 165 kg-PE/mol-V·h by 4b (run 30)] and the activities in the presence of Me2AlCl were higher than those in the presence of Et2AlCl [ex. activity by 4a: 382 kg-PE/mol-V·h (run 25, Me2AlCl) vs. 148 kg-PE/mol-V·h (run 30)]. It also seems likely that the activities were affected by the amount Al employed rather than the Al/V molar ratios in this catalysis (Figure 1). Exclusive formation of polyethylene by 4a,b should be noteworthy, because, as described above, these complexes afforded 1-butene exclusively in the reaction with ethylene in the presence of MAO [17].
Table 3. Reaction of ethylene with V(NR)Cl2[2-ArNCH2(C5H4N)] [R = 1-adamantyl (Ad, 1), 2-MeC6H4 (4), 2,6-Me2C6H3 (5): Ar = 2,6-Me2C6H3 (a), 2,6-iPr2C6H3 (b)]–Me2AlCl, Et2AlCl catalysts a.
Table 3. Reaction of ethylene with V(NR)Cl2[2-ArNCH2(C5H4N)] [R = 1-adamantyl (Ad, 1), 2-MeC6H4 (4), 2,6-Me2C6H3 (5): Ar = 2,6-Me2C6H3 (a), 2,6-iPr2C6H3 (b)]–Me2AlCl, Et2AlCl catalysts a.
RunVanadium complexAl cocat.Al/V bYieldActivity c
R (V cat.)/μmol(mmol) /mg
5d1-adamantyl (1a) e0.5Me2AlCl (0.10)20058.7704
13d1-adamantyl (1a) f1.0Me2AlCl (0.50)500116696
212-MeC6H4 (4a)1.0Me2AlCl (1.0)100016.7100
222-MeC6H4 (4a)1.0Me2AlCl (2.0)200046.4278
232-MeC6H4 (4a)1.0Me2AlCl (3.0)300051.0306
252-MeC6H4 (4a)1.0Me2AlCl (4.0)400063.7382
262-MeC6H4 (4a)1.0Me2AlCl (5.0)500057.8347
272-MeC6H4 (4b)2.0Me2AlCl (1.5)75011.936
282-MeC6H4 (4b)2.0Me2AlCl (2.0)100017.853
292-MeC6H4 (4b)2.0Me2AlCl (2.5)125018.255
302-MeC6H4 (4b)2.0Me2AlCl (3.0)150055.1165
312-MeC6H4 (4b)2.0Me2AlCl (4.0)200054.1162
322-MeC6H4 (4a)1.0Et2AlCl (0.20)2008.149
332-MeC6H4 (4a)1.0Et2AlCl (0.5050011.770
342-MeC6H4 (4a)1.0Et2AlCl (1.0)100011.670
352-MeC6H4 (4a)1.0Et2AlCl (1.5)150024.6148
362-MeC6H4 (4a)1.0Et2AlCl (2.0)200015.995
372-MeC6H4 (4b)1.0Et2AlCl (0.20)2005.533
382-MeC6H4 (4b)1.0Et2AlCl (0.50)5005.131
392-MeC6H4 (4b)1.0Et2AlCl (1.0)100010.161
402-MeC6H4 (4b)1.0Et2AlCl (1.5)15004.024
412-MeC6H4 (4b)1.0Et2AlCl (2.0)20003.219
422,6-Me2C6H3 (5a) g1.0Et2AlCl (0.10)100140840
432,6-Me2C6H3 (5b) g0.2Et2AlCl (0.04)2002006000
a Conditions: toluene 30 mL, ethylene 8 atm., 0 °C, 10 min. b Molar ratio of Al/V. c Activity in kg-PE/mol-V·h. d Data cited from reference [16]. e Mη = 6.76 × 106 measured by viscosity. f Mη = 8.96 × 106 measured by viscosity. g Data cited from reference [10].
Figure 1. Effect of R2AlCl (R = Me, Et) toward the activity in ethylene polymerization by V(N-2-MeC6H4)Cl2[2-(2,6-R'2C6H3)NCH2(C5H4N)] [R' = Me (4a), iPr (4b)]. Details are shown in Table 3.
Figure 1. Effect of R2AlCl (R = Me, Et) toward the activity in ethylene polymerization by V(N-2-MeC6H4)Cl2[2-(2,6-R'2C6H3)NCH2(C5H4N)] [R' = Me (4a), iPr (4b)]. Details are shown in Table 3.
Catalysts 03 00148 g001

3. Experimental Section

3.1. General Procedure

All experiments were carried out under a nitrogen atmosphere in a Vacuum Atmospheres drybox. Anhydrous grade toluene, n-hexane (Kanto Kagaku Co., Ltd. Tokyo, Japan) was transferred into a bottle containing molecular sieves (a mixture of 3A 1/16, 4A 1/8, and 13 × 1/16) in the drybox under nitrogen stream, and were passed through an alumina short column under N2 stream prior to use. Complexes employed here were prepared according to our previous reports [10,15,16,17]. Polymerization grade ethylene (purity > 99.9%, Sumitomo Seika Co. Ltd., Hyogo, Japan) was used as received. Toluene and AlMe3 in the commercially available methylaluminoxane (PMAO-S, 9.5 wt% (Al) toluene solution, Tosoh Finechem Co., Yamaguchi, Japan) were removed under reduced pressure (at ca. 50 °C for removing toluene, AlMe3, and then heated at >100 °C for 1 h for completion) in the drybox to give white solids.

3.2. Ethylene Polymerization

Ethylene polymerizations were conducted in a 100 mL scale stainless steel autoclave. The typical reaction procedure is as follows. Toluene (29 mL) and a prescribed amount of Et2AlCl or Me2AlCl (1 M in n-hexane) were added into the autoclave in the drybox. The reaction apparatus was then filled with ethylene (1 atm.), and catalyst in toluene (1.0 mL) was then added into the autoclave, the reaction apparatus was then immediately pressurized to 7 atm. (total 8 atm.), and the mixture was magnetically stirred for a prescribed time. After the above procedure, ethylene that remained was purged upon cooling, and the mixture was then poured into MeOH containing HCl. The resultant polymer (white precipitate) was collected on a filter paper through filtration, and was adequately washed with MeOH. The resultant polymer was then dried in vacuo at 60 °C for 2 h.

4. Conclusions

In summary, in this paper, we explored ethylene polymerization using V(NR)Cl2(L) [R = 1-adamantyl, L = 2-(2,6-R'2C6H3)NCH2(C5H4N) {1a,b, R' = Me (a), iPr (b)}, 2-(2,6-Me2C6H3)NCH2(C9H6N) (2a), 8-(2,6-Me2C6H3)NCH2(C9H6N) (3a); R = 2-MeC6H4 (4a,b), 2,6-Me2C6H3 (5a,b), L = 2-(2,6-R'2C6H3)NCH2(C5H4N)] in the presence of halogenated Al alkyls. The reaction products were polyethylene that were insoluble in hot O-dichlorobenzene for measurement of molecular weights by GPC in ordinary analysis procedure, suggesting formation of ultrahigh molecular weight polymers as reported previously [8,16]. Moreover, we demonstrated by 1a,b, that the anionic chelate donor ligand plays an essential role for stabilization of catalytically-active species and proposed an assumption that cationic vanadium(V) species play a key role in this catalysis, the facts observed here should be promising and important for designing efficient catalysts for olefin polymerization/dimerization, including the effect of catalyst/cocatalyst nuclearity that would play an important role in this catalysis.

Acknowledgments

This project was partly supported by Bilateral Joint Projects between Japan Society of Promotion of Sciences (JSPS) and National Natural Science Foundation of China (NSFC). Kotohiro Nomura and Atsushi Igarashi express their heartfelt thanks to Tosoh Finechem Co. for donating MAO.

Conflict of Interest

The authors declare no conflict of interest.

References

  1. Hagen, H.; Boersma, J.; van Koten, G. Homogeneous vanadium-based catalysts for the Ziegler–Natta polymerization of α-olefins. Chem. Soc. Rev. 2002, 31, 357–364. [Google Scholar] [CrossRef]
  2. Gambarotta, S. Vanadium-based Ziegler/Natta: Challenges, promises, problems. Coord. Chem. Rev. 2003, 237, 229–243. [Google Scholar] [CrossRef]
  3. Nomura, K.; Zhang, W. (Imido)vanadium(V)-alkyl, -alkylidene complexes exhibiting unique reactivity towards olefins and alcohols. Chem. Sci. 2010, 1, 161–173. [Google Scholar] [CrossRef]
  4. Redshaw, C. Vanadium procatalysts bearing chelating aryloxides: structure–activity trends in ethylene polymerisation. Dalton Trans. 2010, 39, 5595–5604. [Google Scholar] [CrossRef]
  5. Nomura, K.; Zhang, S. Design of vanadium complex catalysts for precise olefin polymerization. Chem. Rev. 2011, 111, 2342–2362. [Google Scholar] [CrossRef]
  6. Nomura, K.; Sagara, A.; Imanishi, Y. Olefin polymerization and ring-opening metathesis polymerization of norbornene by (arylimido)(aryloxo)vanadium(V) complexes of the type VX2(NAr)(OAr¢). Remarkable effect of aluminum cocatalyst for the coordination and insertion and ring-opening metathesis. Macromolecules 2002, 35, 1583–1590. [Google Scholar]
  7. Wang, W.; Nomura, K. Remarkable effects of aluminum cocatalyst and comonomer in ethylene copolymerizations catalyzed by (arylimido)(aryloxo)vanadium complexes: efficient synthesis of high molecular weight ethylene/norbornene copolymer. Macromolecules 2005, 38, 5905–5913. [Google Scholar] [CrossRef]
  8. Wang, W.; Nomura, K. Notable effects of aluminum alkyls and solvents for highly efficient ethylene (co)polymerizations catalyzed by (arylimido)-(aryloxo)vanadium complexes. Adv. Synth. Catal. 2006, 348, 743–750. [Google Scholar] [CrossRef]
  9. Onishi, Y.; Katao, S.; Fujiki, M.; Nomura, K. Synthesis and structural analysis of (arylimido)vanadium(V) complexes containing phenoxyimine ligands: new, efficient catalyst precursors for ethylene polymerization. Organometallics 2008, 27, 2590–2596. [Google Scholar] [CrossRef]
  10. Zhang, S.; Katao, S.; Sun, W.-H.; Nomura, K. Synthesis of (arylimido)vanadium(V) complexes containing (2-anilidomethyl)pyridine ligands and their use as the catalyst precursors for olefin polymerization. Organometallics 2009, 28, 5925–5933. [Google Scholar] [CrossRef]
  11. Macchioni, A. Ion pairing in transition-metal organometallic chemistry. Chem. Rev. 2005, 105, 2039–2073. [Google Scholar] [CrossRef]
  12. Li, H.; Marks, T.J. Nuclearity and cooperativity effects in binuclear catalysts and cocatalysts for olefin polymerization. Proc. Natl. Acad. Sci. USA 2006, 103, 15295–15302. [Google Scholar] [CrossRef]
  13. Bochmann, M. The chemistry of catalyst activation: the case of group 4 polymerization catalysts. Organometallics 2010, 29, 4711–4740. [Google Scholar] [CrossRef]
  14. Christman, D.L. Preparation of polyethylene in solution. J. Polym. Sci. Part A-1 1972, 10, 471–487. [Google Scholar] [CrossRef]
  15. Zhang, S.; Nomura, K. Highly efficient dimerization of ethylene by (imido)vanadium complexes containing (2-anilidomethyl)pyridine ligands: notable ligand effect toward activity and selectivity. J. Am. Chem. Soc. 2010, 132, 4960–4965. [Google Scholar] [CrossRef]
  16. Igarashi, A.; Zhang, S.; Nomura, K. Ethylene dimerization/polymerization catalyzed by (adamantylimido)vanadium(V) complexes containing (2-anilidomethyl)pyridine ligands: factors affecting the ethylene reactivity. Organometallics 2012, 31, 3575–3581. [Google Scholar] [CrossRef]
  17. Nomura, K.; Igarashi, A.; Katao, S.; Zhang, W.; Sun, W.-H. Synthesis and structural analysis of (imido)vanadium(V) complexes containing chelate (anilido)methyl-imine ligands: Ligand effect in ethylene dimerization. Inorg. Chem. 2013, in press. [Google Scholar]
  18. Redshaw, C.; Rowan, M.A.; Homden, D.M.; Dale, S.H.; Elsegood, M.R.J.; Matsui, S.; Matsuura, S. Vanadyl C and N-capped tris(phenolate) complexes: influence of procatalyst geometry on catalytic activity. Chem. Commun. 2006, 3329–3331. [Google Scholar]
  19. Wu, J.-Q.; Mu, J.-S.; Zhang, S.-W.; Li, Y.-S. Vanadium(V) complexes containing tetradentate amine trihydroxy ligands as catalysts for copolymerization of cyclic olefins. J. Polym. Sci. Part A 2010, 48, 1122–1132. [Google Scholar] [CrossRef]
  20. Redshaw, C.; Warford, L.; Dale, S.H.; Elsegood, M.R.J. Vanadyl complexes bearing bi- and triphenolate chelate ligands: highly active ethylene polymerisation procatalysts. Chem. Commun. 2004, 1954–1955. [Google Scholar]
  21. Arbaoui, A.; Redshaw, C.; Homden, D.M.; Wright, J.A.; Elsegood, M.R.J. Vanadium-based imido-alkoxide pro-catalysts bearing bisphenolate ligand for ethylene and e-caprolactone polymerisation. Dalton Trans. 2009, 8911–8922. [Google Scholar]
  22. Redshaw, C.; Rowan, M.A.; Warford, L.; Homden, D.M.; Arbaoui, A.; Elsegood, M.R.J.; Dale, S.H.; Yamato, T.; Casas, C.P.; Matsui, S.; et al. Oxo- and imidovanadium complexes incorporatingmethylene- and diachtungtrenungmethyleneoxa-bridged calix[3]- and achtungtrenung-[4]arenes: synthesis, structures and ethylene polymerisation catalysis. Chem.-Eur. J. 2007, 13, 1090–1107. [Google Scholar]
  23. Homden, D.; Redshaw, C.; Wright, J.A.; Hughes, D.L.; Elsegood, M.R.J. Early transition metal complexes bearing a c-capped tris(phenolate) ligand incorporating a pendant imine arm: synthesis, structure, and ethylene polymerization behavior. Inorg. Chem. 2008, 47, 5799–5814. [Google Scholar] [CrossRef]
  24. Clowes, L.; Redshaw, C.; Hughes, D.L. Vanadium-based pro-catalysts bearing depleted 1,3-calix[4]arenes for ethylene or ε-caprolactone polymerization. Inorg. Chem. 2011, 50, 7838–7845. [Google Scholar] [CrossRef]
Back to TopTop