The influence of ligand on the reaction outcome is depicted in Figure . Different from our previously observed ligand effects for iron-catalyzed C-H activation reactions , where only a certain structure of ligand was uniquely effective, this particular AAPE reaction exhibited a certain level of tolerance to diverse ligand structures. The desired cyclization product 2 was obtained in 25% yield even in the absence of a TP ligand. We speculate that aluminum catecholate may interact with iron in this reaction system to stabilize the iron species in the catalytic cycle . Besides the optimal ligand (TP1), TP2 and triphos were also effective to yield 2 in 88% and 85%, respectively. Interestingly, besides tridentate phosphine ligands; bisphosphine ligands such as dppbz and dppe were also effective to give 5 decent yields. Even tetradentate phosphine ligand (TetraP) gave 2 in 74% yield. In contrast, monodentate phosphine ligand (PPh3) and pyridine-type ligands such as dtbpy or terpy were ineffective. The ligand dependence observed implies the coordination environment of iron in the catalytic cycle varies as ligand dissociation and association may occur 24 , which will be subjected to our further mechanistic studies.