Oxo‐ and Imidovanadium Complexes Incorporating Methylene‐ and Dimethyleneoxa‐Bridged Calix[3]‐ and ‐[4]arenes: Synthesis, Structures and Ethylene Polymerisation Catalysis

Abstract

Reaction of [V(X)(OR)3] (X=O, Np-tolyl; R=Et, nPr or tBu) with p-tert-butylhexahomotrioxacalix[3]areneH3, LH3, affords the air-stable complexes [{V(X)L}n] (X=O, n=1 (1); X=Np-tolyl, n=2 (2)). Alternatively, 1 is readily available either from interaction of [V(mes)3THF] with LH3, and subsequent oxidation with O2 or upon reaction of LLi3 with [VOCl3]. Reaction of [V(Np-tolyl)(OtBu)3] with 1,3-dimethylether-p-tert-butylcalix[4]areneH2, Cax(OMe)2(OH)2, afforded [{VO(OtBu)}2(mu-O)Cax(OMe)2(O)2].2 MeCN (42 MeCN), in which two vanadium atoms are bound to just one calix[4]arene ligand; the n-propoxide analogue of 4, namely [{VO(OnPr)}2(mu-O)Cax(OMe)2(O)2].1.5 MeCN (51.5 MeCN), has also been isolated from a similar reaction using [V(O)(OnPr)3]. Reaction of [VOCl3], LiOtBu, (Me3Si)2O and Cax(OMe)2(OH)2 gave [{VO(OtBu)Cax(OMe)2(O)2}2Li4O2].8 MeCN (68 MeCN), in which an Li4O4 cube (two of the oxygen atoms are derived from the calixarene ligands) is sandwiched between two Cax(OMe)2(O)2. The reaction between [V(Np-tolyl)(OtBu)3] and Cax(OMe)2(OH)2, afforded [V(Np-tolyl)(OtBu)2Cax(OMe)2(O)(OH)]5 MeCN (75 MeCN), in which two tert-butoxide groups remain bound to the tetrahedral vanadium atom, which itself is bound to the calix[4]arene through only one phenolic oxygen atom. Reaction of p-tert-butylcalix[4]areneH4, Cax(OH)4 and [V(Np-tolyl)(OnPr)3] led to loss of the imido group and formation of the dimeric complex [{VCax(O)4(NCMe)}2].6 MeCN (86 MeCN). Monomeric vanadyl oxo- and imidocalix[4]arene complexes [V(X)Cax(O)3(OMe)(NCMe)] (X=O (11), Np-tolyl (12)) were obtained by the reaction of the methylether-p-tert-butylcalix[4]areneH3, Cax(OMe)(OH)3, and [V(X)(OR)3] (R=Et or nPr). Vanadyl calix[4]arene fragments can be linked by the reaction of 2,6-bis(bromomethyl)pyridine with Cax(OH)4 and subsequent treatment with [VOCl3] to afford the complex [{VOCax(O)4}2(mu-2,6-(CH2)2C5H3N)].4 MeCN (134 MeCN). The compounds 1-13 have been structurally characterised by single-crystal X-ray diffraction. Upon activation with methylaluminoxane, these complexes displayed poor activities, however, the use of dimethylaluminium chloride and the reactivator ethyltrichloroacetate generates highly active, thermally stable catalysts for the conversion of ethylene to, at 25 degrees C, ultra-high-molecular-weight (>5, 500,000), linear polyethylene, whilst at higher temperature (80 degrees C), the molecular weight of the polyethylene drops to about 450,000. Using 1 and 2 at 25 degrees C for ethylene/propylene co-polymerisation (50:50 feed) leads to ultra-high-molecular-weight (>2,900,000) polymer with about 14.5 mol% propylene incorporation. The catalytic systems employing the methyleneoxa-bridged complexes 1 and 2 are an order of magnitude more active than the bimetallic complexes 5 and 13, which, in turn, are an order of magnitude more active than pro-catalysts 8, 11 and 12. These differences in activity are discussed in terms of the structures of each class of complex.

Use of Metal Catalysts Bearing Schiff Base Macrocycles for the Ring Opening Polymerization (ROP) of Cyclic Esters

“…for these systems that the presence of the oxygen bridge in the macrocycle can help to stabilize the catalytically-active species, a situation reminiscent of the vanadium-based calixarene polymerization catalysis of ethylene [31]. When these systems were employed for the ROP of rac-lactide, best conversions were achieved at 110 °C with the ratio 100:1:1 (rac-LA:Al:BnOH) over 12 h. For organoaluminium systems, the ROP of lactide often requires more robust conditions than those employed for ε-CL [32].…”

“…Furthermore, the systems 27 and 29 exhibit an induction period that, following a 15%-20% Scheme 7. Zinc complexes (27)(28)(29)(30)(31)(32).…”

Niobium‐ and Tantalum‐Based Ethylene Polymerisation Catalysts Bearing Methylene‐ or Dimethyleneoxa‐Bridged Calixarene Ligands

“…Under the same catalytic conditions, vanadyl complexes bearing methylene-bridged (-CH 2 -) calix [4]arenes proved to have far inferior activities, though still far better than those observed previously for calix [4]arene-based systems. [3] Herein, we extend these studies to the other Group 5 metals, niobium and tantalum, and report the synthesis, characterisation and ethylene polymerisation behaviour of calix[n]arenes (n = 4, 6 and 8), and compare this behaviour with that of related oxacalix [3]arene complexes. Metallocalix[n]arenes incorporating niobium or tantalum are rather rare, with reports restricted to the calix [4]arene work of Floriani and co-workers [4] and more recently Radius and co-workers.…”

“…[2] However, recently we have found that vanadyl complexes bearing dimethyleneoxa-bridged (-CH 2 OCH 2 -) oxacalix [3]arenes form extremely active catalytic species upon interaction with dimethylaluminium chloride (DMAC) in the presence of the re-activator ethyl trichloroacetate (ETA). Under the same catalytic conditions, vanadyl complexes bearing methylene-bridged (-CH 2 -) calix [4]arenes proved to have far inferior activities, though still far better than those observed previously for calix [4]arene-based systems.…”

Ethylene Polymerization Using (Imino)vanadium(V) Dichloride Complexes Containing (Anilido)methyl-pyridine, -quinoline Ligands–Halogenated Al Alkyls Catalyst Systems

“…Moreover, we prepared the adamantylimido complexes containing 2-or 8-(anilidomethyl)-quinoline ligands, V(NAd)Cl 2 [(2,6-Me 2 C 6 H 3 )NCH 2 (C 9 H 6 N)] (2a,3a, Scheme 2), and V(N-2-MeC 6 H 4 )Cl 2 [2-ArNCH 2 (C 5 H 4 N)] 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 Et 2 AlCl or Me 2 AlCl 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]. Scheme 2.…”