Vanadium complexes derived from oxacalix[6]arenes: structural studies and use in the ring opening homo-/co-polymerization of ε-caprolactone/δ-valerolactone and ethylene polymerization

Reaction of Na[VO(tBuO)(4)] (generated in situ from VOCl3 and NaOtBu) with p-tert-butyltetrahomodioxacalix[6]areneH(6) ((LH6)-H-1) afforded, after work-up (in MeCN), the mixed-metal complex [(VO)(2)(mu-O)Na-2(L-1)(MeCN)(4)]center dot 5(MeCN) (1 center dot 5MeCN), whilst the oxo complex {[VO](4)L-1} (2 center dot 6MeCN) was isolated via the use of [VO(OnPr)(3)]. Reaction of (LH6)-H-1 with [V(Np-CH3C6H4)(OtBu)(3)] afforded the complex {[V(Np-CH3C6H4)](2)L-1} (3 center dot 7MeCN center dot 0.5CH(2)Cl(2)). Use of similar methodology afforded the imido complexes {[V(Np-RC6H4)](2)L-1} (R = OMe (4); CF3 (5); Cl (6); F (7)); on one occasion, reaction of [V(Np-CH3C6H4)(OEt)(3)] with (LH6)-H-1 afforded the product [VO(L-2)](2)center dot 4MeCN (8 center dot 4MeCN) (L-2 = 2-(p-CH3-C6H4NCH)-4-tBu-C6H2O-6-CH2)-4-tBuC(6)H(2)OH) in which L-1 has been cleaved. For comparative catalytic ring opening polymerization (ROP) studies, the known complexes [VOL3] (L-3 = oxacalix[3]arene) (I), [V(Np-CH3-C6H4)L-3](2) (II), [Li(MeCN)(4)][V-2(O)(2)Li(MeCN)((LH2)-H-6)(2)] ((LH6)-H-6 = p-tert-butylcalix[6]areneH(6)) (III) and [(VO)(2)(LH)-H-8] ((LH8)-H-8 = p-tert-butylcalix[8]areneH(8)) (IV) have also been prepared. ROP studies, with or without external alcohol present, indicated that complexes 1 to 8 exhibited moderate to good conversions for epsilon-Cl, delta-VL and the co-polymerization thereof. Within the imido series, a positive influence was observed when electron withdrawing substituents were present. These systems afforded relatively low molecular weight products and were also inactive toward the ROP of rac-lactide. In the case of ethylene polymerization, complexes 3, 5 and 7 exhibited highest activity when screened in the presence of dimethylaluminium chloride/ethyltrichloroacetate; the activity of 4 was much lower. The products were highly linear polyethylene with M-w in the range 74-120 x 10(3) Da.