Four- and five-coordinate aluminum ketiminate complexes: Synthesis, characterization, and ring-opening polymerization

A series of aluminum complexes featuring with the ketiminate ligand, OCMeCHCMeNHAr (Ar = 2,6-(Pr2C6H3)-Pr-i, 1), have been prepared and characterized spectroscopically and structurally. Reactions of 1 with trialkylaluminum in 1:1 or 1:2 molar ratio generate four- and five-coordinated aluminum complexes (OCMeCHCMeNAr)AlR2 (R = Me (2); R = Et (3)) and (OCMeCHCMeNAr)(2)AlR (R = Me (4); R = Et (5)) in high yields, Similarly, reaction of AlCl3 with 1 or 2 equiv of the lithiated 1 in toluene afforded bis(ketiminate) aluminum chloride complex, (OCMeCHCMeNAr)(2)AlCl (6) or (OCMeCHCMeNAr)AlCl2 (7). Surprisingly, reacting 6 with 1 equiv of AgBF4 in methylene/acetonitrile mix-solvents generates (OCMeCHCMeNAr)(2)AlF (8) in moderate yield. The structures of complexes 2-6 and 8 have been determined by X-ray crystallography. Complexes 2 and 3 both exhibit tetrahedron structures with the aluminum atom surrounded by oxygen and nitrogen atoms of chelating ketiminate and two alkyl groups. The mono- and bis-ketiminate aluminum complexes 2-5 have shown moderate activity toward the ring-opening polymerization of E-caprolactone.