title: Potassium, zinc, and magnesium complexes of a bulky OOO-tridentate bis(phenolate) ligand: synthesis, structures, and studies of cyclic ester polymerisation.
abstract: Reaction of the OOO-coordinating tridentate bis(phenolate) protio-ligand 2,2'-{oxybis(methylene)}bis{4,6-di(1-methyl-1-phenylethyl)phenol} (L(O3)-H2), with 1 equiv. of KN(SiMe3)2 in toluene or THF yielded [K(L(O3)-H)] (1) or [K(L(O3)-H)(THF)] (2), respectively. Single-crystal X-ray diffraction studies of 1 and 2 revealed mononuclear structures with the phenyl rings of the bulky ligand displaying stabilising π-interactions to the potassium centre. L(O3)-H2 also reacts with 1 equiv. of ZnEt2 or Mg(n)Bu2 to give [M2(L(O3))2] (M = Zn (3) or Mg (4)) in good yield. The molecular structures of complex 3 and 4 reveal dinuclear species in which the metal centres are tetra-coordinated to the three oxygen atoms of one L(O3) ligand, and to the bridging oxygen atom of one phenolate group of another. Complexes 1-4 are catalysts for ring-opening polymerisation of ε-caprolactone and L- and rac-lactide in the presence of benzyl alcohol (BnOH) and also other initiators to give the corresponding polyesters. Kinetic studies for the ROP of ε-caprolactone using 3 and BnOH gives an unusual rate expression R(p) = -d[CL]/dt = k(p)[BnOH]0[3]0(0.5) for which a tentative kinetic model is proposed.
authors: Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, Gansu, PR China. huangyong@lzu.edu.cn
authors: Yong
authors: Y
authors: Huang
authors: Wei
authors: W
authors: Wang
authors: Chu-Chieh
authors: CC
authors: Lin
authors: Matthew P
authors: MP
authors: Blake
authors: Lawrence
authors: L
authors: Clark
authors: Andrew D
authors: AD
authors: Schwarz
authors: Philip
authors: P
authors: Mountford
mesh_terms: D002208:Caproates / Q000737:chemistry; D002384:Catalysis; D004146:Dioxanes / Q000737:chemistry; D004952:Esters / Q000737:chemistry*; D007783:Lactones / Q000737:chemistry; D008024:Ligands; D008274:Magnesium / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D058105:Polymerization; D011188:Potassium / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D002208:Caproates; D004146:Dioxanes; D004952:Esters; D007783:Lactones; D008024:Ligands; D009942:Organometallic Compounds; D010636:Phenols; C121056:caprolactone; C091880:dilactide; D008274:Magnesium; D015032:Zinc; D011188:Potassium