The reaction of 2-phenoxyethanol with AlX3 affords a five-coordinated dimeric product [(μ-OCH2CH2OPh)AlX2]2 (1, X=Cl; 2, X=Br) in high yields. However, the reaction of 2-phenoxyethanol with Al(Bui)3 yields a four-coordinated dimeric product [(μ-O(CH2)2OPh)Al(Bui)2] 2 (3). A mixture, [(μ-O(CH2)2OPh)Al(Et)0.75(Cl) 1.25]2 (4) is obtained from the reaction of 2-phenoxyethanol with one equivalent of Et2AlCl. The reaction of 2-methoxybenzyl alcohol with AlR3 gives a semi-pentacoordinated dimeric product [(μ-OCH2C6H4OMe)AlR2]2 (5, R=Me; 6, X=Bui) in high yields. Crystal structure studies of these compounds reveal that the distance between Al and the phenoxy oxygen or the methoxy oxygen is 3>6>5≫4>1~2. Although both the electronic and steric effect influence the nature of the O,O′-bifunctional ligand chelating on the aluminum center to generate a five- or four-coordinated aluminum, the electronic effect is considered to play a major role. The interaction of aluminum and ethereal oxygen can be monitored by 13C-NMR spectroscopic studies.
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