Molecular Design of Single Site Catalyst Precursors for the Ring-Opening Polymerization of Cyclic Ethers and Esters. 2. Can Ring-Opening Polymerization of Propylene Oxide Occur by a Cis-Migratory Mechanism?

Abstract

From the reactions between 2,2‘-ethylidenebis(4,6-di-tert-butylphenol) and 2,2‘-methylidenebis(4-dimethyl-6-di-tert-butylphenol) and Et2AlCl the biphenoxide complexes [(O∼∼CHMe∼∼O)AlCl]2, 1, and [(O∼∼CH2∼∼O)AlCl]2, 2, have been isolated and characterized. These dimers are broken up by donor ligands, and the molecular structure of ethylidenebis(4,6-di-tert-butylphenoxide)AlCl(THF), 3, has been structurally characterized. Racemic 5,5‘-6,6‘-tetramethyl-3,3‘-di-tert-butyl-1,1‘-biphen-2,2‘-diol and Et2AlCl react in hexane to give [(O∼∼O)AlCl]2, compound 6, as a hydrocarbon insoluble white precipitate. In the donor solvent THF monomeric species are formed, and (O∼∼O)AlX(THF) has been crystallographically characterized, X = 20% Cl and 80% Et occupancy. Refluxing in THF favors X = Cl, compound 4. The reaction of Et2Al(OEt) with the biphenol gives (O∼∼O)AlEt(THF), 5, in the presence of THF by displacement of one ethyl and one ethoxide ligand. Compounds 1, 2, 3, 4, 5, 6, [(O∼∼CHMe∼∼O)Al(OiPr-d7)]2, and [Cp2Zr(OEt)(...