Some crown ether chemistry of Ti, Zr and Hf derived from liquid clathrate media

The reaction of [Ti(η-C5H5)2Cl2] with HCl(g) in the presence of 18-crown-6 formed the oxonium ion-containing complex [H3O+·18-crown-6][TiCl5(H2O)–] 1. Its crystal structure shows the oxonium ion resides within the crown ether and has a pyramidal structure. Treatment of [Ti(η-C5H5)Cl3] with AlMe3 in the presence of 18-crown-6 resulted in the formation of the titanium(III) complex [Ti(η-C5H5)Cl+·18-crown-6][AlCl2Me2] 2. The structure of 2 reveals a cation with a five-co-ordinate Ti where the centroid of the C5H5 ring occupies the apex of a square pyramid. The crown ether 18-crown-6 underwent C–O bond scission by treatment with ZrCl4 in the presence of thf (tetrahydrofuran) to form the ring-opened zirconium(IV) co-ordination complex [ZrCl2·(OCH2CH2)5OCH2CH2Cl+][ZrCl5(thf)–] 3. The structure of 3 shows the formation of a zirconium alkoxide species formed by the ring-opening reaction. The seven-co-ordinate zirconium center has pentagonal-bipyramidal geometry with two chloride atoms in the axial positions. In an analogous reaction, but in the presence of NaCl, HfCl4 formed the ionic complex [Na+·18-crown-6][HfCl5(thf)–] 4, which has a structure similar to that of 1.