Reaction of Na[VO(tBuO) ] (generatedin situfrom VOCl and NaOtBu) withp-tert-butyltetrahomodioxacalix[6]areneH (L H ) afforded, after work-up (in MeCN), the mixed-metal complex [(VO) (μ-O)Na (L )(MeCN) ]·5(MeCN) (1·5MeCN), whilst the oxo complex {[VO] L } (2·6MeCN) was isolatedviathe use of [VO(OnPr) ]. Reaction of L H with [V(Np-CH C H )(OtBu) ] afforded the complex {[V(Np-CH C H )] L } (3·7MeCN·0.5CH Cl ). Use of similar methodology afforded the imido complexes {[V(Np-RC H )] L } (R = OMe (4); CF (5); Cl (6); F (7)); on one occasion, reaction of [V(Np-CH C H )(OEt) ] with L H afforded the product [VO(L )] ·4MeCN (8·4MeCN) (L = 2-(p-CH -C H NCH)-4-tBu-C H O-6-CH )-4-tBuC H OH) in which L has been cleaved. For comparative catalytic ring opening polymerization (ROP) studies, the known complexes [VOL ] (L = oxacalix[3]arene) (I), [V(Np-CH -C H )L ] (II), [Li(MeCN) ][V (O) Li(MeCN)(L H ) ] (L H =p-tert-butylcalix[6]areneH ) (III) and [(VO) L H] (L H =p-tert-butylcalix[8]areneH ) (IV) have also been prepared. ROP studies, with or without external alcohol present, indicated that complexes1to8exhibited moderate to good conversions for ε-Cl, δ-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 ofrac-lactide. In the case of ethylene polymerization, complexes3,5and7exhibited highest activity when screened in the presence of dimethylaluminium chloride/ethyltrichloroacetate; the activity of4was much lower. The products were highly linear polyethylene withM in the range 74-120 × 10 Da. 4 3 6 6 2 2 4 4 3 6 3 6 4 3 3 6 4 2 2 2 6 4 2 3 3 6 4 3 6 2 3 6 4 6 2 2 6 2 3 6 4 2 4 2 2 2 2 6 6 2 8 8 w 1 1 1 1 1 1 1 2 2 1 3 3 3 6 6 8 8 3