A series of novel claw-type aminophenolate zinc chlorides Zn1~Zn8 were synthesized via the reactions of the corresponding sodium salts of the proligands H^1-8L with one equiv. of zinc dichloride at room temperature respectively. All the complexes were characterized by ¹H NMR, ¹³C NMR spectroscopy and elemental analyses. The X-ray diffraction analysis of complex Zn2 showed that, being obtained as a pair of racemic isomers (with configurations of S_NS_Zn and R_NR_Zn), the complex possesses a mononuclear structure and the zinc center is four-coordinated by the tridentate aminophenolate ligand and one chloride ligand in the solid state. When bis(triphenylphosphine)iminium chloride (PPNCl) was used as a co-catalyst, all of these zinc complexes showed high catalytic activities and high selectivities for the formation of polyesters (>99%) in the ring-opening copolymerization (ROCOP) of cyclohexene oxide (CHO) and phthalic anhydride (PA), giving alternative copolymers with narrow molecular weight distributions (PDI=1.14~1.24). The steric hindrance of the substituents on the ligand has an important influence on the catalytic activity of the complex. Zn4 with cumyl groups on the ligand that make the metal center more crowded showed a lower activity than Zn3 at 80 ℃ (Zn3, TOF_PA=400 h^-1, Zn4, TOF_PA=384 h^-1). Moreover, the electron-withdrawing effect of the substituents increased the catalytic activity of the catalyst. For example, under the same conditions, Zn1 with electron-withdrawing substituents took only 22 min to achieve 90% conversion of PA, while Zn2 took 26 min to achieve 87% conversion of PA. Complex Zn1 showed the highest catalytic activity in the copolymerization of CHO and PA (TOF=490 h^-1). In addition, with the increase of the amount of PPNCl, the selectivity of complexes for ester linkages gradually increased. For instance, when one equiv. of PPNCl was added, the selectivity of Zn2 for ester linkages was 96%, while a selectivity of 99% was achieved with the addition of 5 equiv. of PPNCl. All the complexes were also applied in the ROCOP of rac-epichlorohydrin (rac-ECH) and PA, and showed high catalytic activities and high selectivities for polyesters (>99%), but with somewhat wide molecular weight distributions (PDI=1.36~1.49). Complex Zn1 also proved to be the most active one (TOF=848 h^-1). Compared with those for CHO and PA copolymerization, the catalytic activities of the complexes toward the ROCOP of rac-ECH and PA were higher (e.g. Zn2, TOF=402 h^-1, CHO/PA; TOF=745 h^-1, ECH/PA). Further studies suggested that the ROCOP was likely initiated through the ring-opening of epoxides upon the attack of an nucleophilic reagent, for instance, Cl^-.

Key words: claw-type aminophenolate zinc chlorides, epoxide, anhydride, copolymerization, selectivity for ester linkage