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

The trinuclear zinc calix[4]arene complexes [Zn 3 (O 2 CCH 3 ) 2 (L(O) 2 (OMe) 2 ) 2 · x MeCN ( x = 7.5, 1; x = 6, 1'), [Zn 3 (O 2 CCH 3 ) 2 (L(O) 2 (O n Pr) 2 ) 2 ·5MeCN (2·5MeCN), [Zn 3 (OEt) 2 (L(O) 2 (OMe) 2 ) 2 ]·4MeCN (3·4MeCN), [Zn 3 (OEt) 2 (L(Opentyl) 2 ) 2 ]·4.5MeCN (4·4.5MeCN) and [Zn 3 (OH) 2 (L(O) 2 (O n -pentyl) 2 ]·8MeCN (5·8MeCN) 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 5 via a controlled hydrolysis led only to the isolation of polymorphs of (L(OH) 2 (Opentyl) 2 ·MeCN. Reaction of [Zn(C 6 F 5 ) 2 ] with L(OH) 2 (Opentyl) 2 , in the presence of K 2 CO 3 , led to the isolation of the complex [Zn 6 (L(O n -pentyl)) 2 (OH) 3 (C 6 F 5 ) 3 (NCMe) 3 ]·3MeCN (6·3MeCN). The molecular structures of 1-6 reveal they all contain a near linear (163 to 179°) 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 ε-caprolactone at 90 °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 ≈ 2 ≈ 1 > 3.