Vanadyl calix[6]arene complexes: synthesis, structural studies and ethylene homo-(co-)polymerization capability

Treatment of p-tert-butylcalix[6]areneH(6) ((LH6)-H-6) with in situ [LiVO(Ot-Bu)(4)] afforded, after work-up, the dark green complex [Li(MeCN)(4)][V-2(O)(2)Li(MeCN)((LH2)-H-6)(2)]center dot 8MeCN (1 center dot 8MeCN). On one occasion, the reaction led to the formation of a mixture of products, the bulk of which differing from 1 only in the amount of solvate, viz. 2 center dot 9.67MeCN. The second minor, yellow product has the formula {[(VO2)(2)((LH2)-H-6)(Li(MeCN)(2))(2)]center dot 2MeCN}(n) (3 center dot 2MeCN), and comprises a 1D polymeric structure with links through the (LH2)-H-6 ligand and Li2O2 units. When the reverse order of addition was employed such that lithium tert-butoxide (7.5 equivalents) was added to (LH6)-H-6, and subsequently treated with VOCl3 (2 equiv.), the complex {[VO(THF)][VO(mu-O)](2)Li(THF)(Et2O)][L-6]}center dot 2Et(2)O center dot 0.5THF (4 center dot 2Et(2)O center dot 0.5THF), which contains a trinuclear motif possessing a central, octahedral vanadyl centre linked via oxo bridges to two tetrahedral (C-3v) vanadyl centres, was isolated. The calix[6] arene in 4 is severely twisted and adopts a 'down, down, down, down, out, out' conformation. Use of excess lithium tert-butoxide led to a complex very similar to 4, differing only in the solvent of crystallization, namely 5 center dot t(2)O center dot 2THF. The ability of 1 and 5 to act as pre-catalysts for ethylene polymerization in the presence of a variety of co-catalysts and under various conditions has been investigated. Co-polymerization of ethylene with propylene and with 1-hexene have also been conducted; results are compared versus VO(OEt) Cl-2.