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

Abstract

Reaction of TiCl₄ with L–L [L–L = MeE(CH₂)_nEMe; E = S or Se, n = 2 or 3, PhE(CH₂)₂EPh or o-C₆H₄(EMe)₂] in anhydrous n-hexane solution under an N₂ 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)_nEMe or o-C₆H₄(EMe)₂; X = I; L–L = MeSe(CH₂)₂SeMe 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)₂SMe}], [TiCl₄{MeS(CH₂)₃SMe}], [TiCl₄{MeSe(CH₂)₃SeMe}] 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 ≈ 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)₂SMe}]₂(μ-O), formed by partial hydrolysis of [TiCl₄{MeS(CH₂)₂SMe}], has also been identified crystallographically.