Oxo- and imidovanadium complexes incorporating methylene- and dimethyleneoxa-bridged calix[3]- and -[4]arenes: Synthesis, structures and ethylene polymerisation catalysis

Reaction of [V(X)(OR)31 (X=O, Np-tolyl; R=Et, nPr or tBu) with p-tert-butylhexahomotrioxacalix[3]areneH(3), LH3, affords the airstable 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)(3)THF] with LH3, and subsequent oxidation with 0, or upon reaction of LLi3 with [VOCl3] Reaction of [V(Np-tolyl)(OtBu)(3)] with 1,3-dimethylether-p-tert-butylcalix[4]areneH(2), Cax(OMe)(2)(OH)(2), afforded [{VO(OtBu)}(2)(mu-O)Cax(OMe)(2)(O)(2)] center dot 2MeCN (4 center dot 2MeCN), 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)]center dot 1.5 MeCN (5(.)1.5 MeCN), has also been isolated from a similar reaction using [V(O)(OnPr),]. Reaction Of [VOCl3], LiOtBu, (Me3S)(2)O and Cax-(OMe)(2)(OH)(2) gave [{VO(OtBu)Cax-(OMe)(2)(O)(2)}(2)Li4O2]center dot 8 MeCN (6(.)8MeCN), 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)(2)Cax-(OMe)(2)(O)(OH)](.)5MeCN (7.5MeCN), 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]areneH(4), 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)](.)6MeCN (8-6MeCN). 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]arene- H-3, 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 2,6-(CH2)(2)C5H3N)](.)4MeCN (13(.)4MeCN). 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 (> 5500000), linear polyethylene, whilst at higher temperature (80 degrees C), the molecular weight of the polyethylene drops to about 450000. Using I and 2 at 25 degrees C for ethylene/ propylene co-polymerisation (50:50 feed) leads to ultra-high-molecular-weight (> 2900000) 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 1-2. These differences in activity are discussed in terms of the structres of each class of complex.