Aluminum and Titanium Complexes Containing Pyrrole-imine Ligands: Syntheses,Structures, and Ring-opening Polymerization of ε-Caprolactone

Syntheses and properties of aluminum and titanium complexes incorporating the pyrrole-imine ligands, N-((~1H-pyrrol-2-yl)methyl)-1-(~1H-pyrrol-2-yl)methanimine(H_2L1) and 2-cyano-~1H-pyrrole(HL2), have been investigated. Addition of one equiv of H_2L1 to AlMe3 and AlEt_3, respectively results in the formation of dinuclear complexes [Al2(L1)2 Me2](1) and [Al2(L1)2 Et2](2). Treatment of Ti(NMe2)4 with one equiv of HL2 and two equiv of iPrOH or three equiv of BnOH results in the production of complexes [Ti(HL3)2(OiPr)2](3) and [Ti2(HL3)2(OBn)6](4)(H_2L~3 = N,N-dimethyl-~1H-pyrrole-2-carboximid-amide). HL_3 anion is an intermediate which is in situ formed from the reaction of HL2 and Ti(NMe2)4. The structures of 1～4 were characterized by single crystal X-ray diffraction. The catalytic properties of 1～4 toward ring-opening polymerization(ROP) of ε-caprolactone were studied. All of the compounds could effectively initiate the polymerization reactions with good activities.