Bimetallic aluminum complexes bearing novel spiro-phenanthrene-monoketone/OH derivatives: synthesis, characterization and the ring-opening polymerization of ε-caprolactone.

A series of spiro-phenanthrene-monoketone/OH derivatives (L1-L6) were synthesized and fully characterized with H/C NMR spectroscopy and elemental analyses. By treating ligands with AlMe, oxygen-bridged binuclear aluminum complexes (Al1-Al6) were isolated and characterized by H/C NMR spectroscopy. The molecular structures of ligands (L2, L4 and L5) and complex Al1 were determined by single crystal X-ray diffraction. In the presence of benzyl alcohol (BnOH), these aluminum complexes demonstrated high efficiency towards the ring-opening polymerization of ε-caprolactone (ε-CL), resulting in PCL in a linear manner with the BnO-end group. In addition, complexes Al1 and Al5 exhibited good catalytic activities even without BnOH. Moreover, complexes Al3 and Al6 with the bulkier substituent of Pr at the -position of the arylamines demonstrated better catalytic activities than the analogs. Moreover, substituents on the backbone also affected catalytic behaviors.