EXPERIMENTAL AND THEORETICAL APPROACH TO THE UNDERSTANDING OF TICL4 INTERACTING WITH ARENES - ISOLATION OF A D(0)-METAL ARENE COMPLEX AND CYCLOTRIMERIZATION OF BUT-2-YNE PROMOTED BY TICL4

The reaction of TiCl4 with C6Me6 in CH2Cl2 or 1,2-C6H4Cl2 led to a d0- arene complex [(eta6-C6Me6)TiCl3]+[Ti2Cl9]-(2), which was structurally characterized by an X-ray analysis. The structure consists of a three -leg piano-stool metallic fragment (TiCl3)+ eta6 binding the arene moi ety. The H-1 NMR-spectrum of the reaction solution indicated the prese nce of a charge transfer intermediate. The high stability of 2 is evid enced by the TiCl4-promoted stoichiometric cyclotrimerization of but-2 -yne. The theoretical calculations on the model compounds [(eta6-C6H6) TiX3]+ (X = H, F, Cl) and [(176-C6H6)TiX3] (X = F, Cl) explain the hig h stability of the titanium(IV) derivatives, as well as the weaker are ne-metal interaction in the titanium(III) derivatives. Also, a strong positive charge was found on the benzene hydrogens, consistent with an electrophilic activation of the benzene ring. Theoretical calculation s have been carried out on some possible precursors to 2, like [(eta6- C6H6)TiCl4], [(eta2-C6H6)TiCl4], and [Cl3Ti-Cl...eta6-C6H6]. Crystallo graphic details: 2 is orthorhombic, space group Pca2(1), with a = 17.2 63(2) angstrom, b = 8.712(1) angstrom, c = 17.256(2) angstrom, alpha = beta = gamma = 90-degrees, Z = 4, and R = 0.059.