Hard/soft interactions in early transition metal chemistry: synthesis, properties and structures of thioether and selenoether complexes of titanium(IV)

Reaction of TiCl4 with L-L [L-L=MeE(CH2)(n)EMe; E=S or Se, n=2 or 3, PhE(CH2)(2)EPh or o-C6H4(EMe)(2)] in anhydrous n-hexane solution under an N-2 atmosphere results in the rapid formation of [TiCl4(L-L)] as yellow, orange or red solids. Analogous bromo and iodo species, [TiX4(L-L)] [X=Br; L-L=MeE(CH2)(n)EMe or o-C6H4(EMe)(2); X=I; L-L=MeSe(CH2)(2)SeMe or o-C6H4(SeMe)(2)], were obtained as intense orange or red coloured solids by treatment of TiX4 with L-L in CH2Cl2 solution. Crystallographic studies on [TiCl4{MeS(CH2)(2)SMe}], [TiCl4{MeS(CH2)(3)SMe}], [TiCl4{MeSe(CH2)(3)SeMe}] and [TiCl4{o-C6H4(SeMe)(2)}] reveal a distorted octahedral arrangement with the coordinated group 16 donor ligand adopting the DL form in the first three cases and the meso form in the fourth example. These studies also reveal a trans influence series of Cl > S approximate to Se on Ti(IV). Solution NMR studies show that the chloro-compounds undergo rapid pyramidal inversion at ambient temperature, while the bromo and iodo species also undergo rapid ligand dissociation/chelate ring-opening. At low temperature these processes are slowed significantly, such that in most of the chloro and bromo species it is possible to identify both the meso and DL invertomers, although ligand exchange is still rapid at 200 K for the iodo species. The potential of these compounds as sources of titanium sulfide or titanium selenide phases via controlled decomposition is also discussed briefly. Finally, the dinuclear species, [Cl3Ti{MeS(CH2)(2)SMe}](2)(mu-O), formed by partial hydrolysis of [TiCl4{MeS(CH2)(2)SMe}], has also been identified crystallographically.