Inverse Sandwich Arene-Bridged Titanium Complexes Supported by a Bulky Tridentate [O, P, O] Ligand

A bulky tridentate bis(3-methyl-5-arylhydroxyphenyl)phenylphosphine (aryl = 2,4,6-tri-isopropylbenzene, Tipp[O, P, O]) ligand 1 was synthesized. Reaction of 1 with TiCl3(THF)3 (THF = tetrahydrofuran) afforded bis{Tipp[O, P, O] titanium (THF)0.59(Et2O)0.41(mu-chloro)} (2). By reducing 2 with KC8 in toluene or C6D6, two arene-bridged dititanium complexes{Tipp[O, P, O]}2 titanium (mu-eta 6:eta 6-C6H5Me) (3) and {Tipp[O, P, O]}2 titanium (THF)0.58(Et2O)0.42(mu-eta 6:eta 6-C6D6) (4) were obtained, respectively, and structurally characterized. Complexes 3 and 4 featured an inverted sandwich-type structure consisting of a distorted eta 6-toluene or eta 6-benzene unit. Density functional theory calculations analyzed the reason for the loss of aromaticity in the distorted aromatic rings.