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)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(μ‐O)Cax(OMe)2(O)2] ⋅2 MeCN (4⋅2 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(μ‐O)Cax(OMe)2(O)2]⋅1.5 MeCN (5⋅1.5 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 (6⋅8 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 (7⋅5 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 (8⋅6 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(μ‐2,6‐(CH2)2C5H3N)]⋅4 MeCN (13⋅4 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 °C, ultra‐high‐molecular‐weight (> 5 500 000), linear polyethylene, whilst at higher temperature (80 °C), the molecular weight of the polyethylene drops to about 450 000. Using 1 and 2 at 25 °C for ethylene/propylene co‐polyme