Trinuclear zinc calix[4]arenes: synthesis, structure, and ring opening polymerization studies

The trinuclear zinc calix[4]arene complexes [Zn-3(O2CCH3)(2)(L(O)(2)(OMe)(2))(2)center dot xMeCN (x = 7.5, 1; x = 6, 1 '), [Zn-3(O2CCH3)(2)(L(O)(2)(OnPr)(2))(2)center dot 5MeCN (2 center dot 5MeCN), [Zn-3(OEt)(2)(L(O)(2)(OMe)(2))(2)]center dot 4MeCN (3 center dot 4MeCN), [Zn-3(OEt)(2)(L(Opentyl)(2))(2)]center dot 4.5MeCN (4 center dot 4.5MeCN) and [Zn-3(OH)(2)(L(O)(2)(On-pentyl)(2)]center dot 8MeCN (5 center dot 8MeCN) have been isolated from reaction of [(ZnEt)(2)(L(O)(2)(OR)(2))(2)] (L(OH)(2)(OR)(2) = 1,3-dialkoxy-4-tert-butylcalix[4]arene; R = methyl, n-propyl or pentyl) and the reagents acetic acid, ethanol, and presumed adventitious water, respectively. Attempts to make 5via a controlled hydrolysis led only to the isolation of polymorphs of (L(OH)(2)(Opentyl)(2)center dot MeCN. Reaction of [Zn(C6F5)(2)] with L(OH)(2)(Opentyl)(2), in the presence of K2CO3, led to the isolation of the complex [Zn-6(L(On-pentyl))(2)(OH)(3)(C6F5)(3)(NCMe)(3)]center dot 3MeCN (6 center dot 3MeCN). The molecular structures of 1-6 reveal they all contain a near linear (163 to 179 degrees) Zn-3 motif. In 1-5, a central tetrahedral Zn centre is flanked by trigonal bipyramidal Zn centres, whilst in 6, for the linear Zn-3 unit, a central distorted octahedral zinc centre is flanked by trigonal planar and a tetrahedral zinc centres. Screening for the ring opening polymerization (ROP) of epsilon-caprolactone at 90 degrees C revealed that they are active with moderate to good conversion affording low to medium molecular weight products with at least two series of ions. For comparative studies, the trinuclear aminebis(phenolate) complex [Zn-3(Oi-Pr)(2)L-/] (L-/ = n-propylamine-N,N-bis(2-methylene-4,6-di-tert-butylphenolate) I was prepared. Kinetics revealed the rate order I > 4 > 6 approximate to 2 approximate to 1 > 3.