Oxidation of Titanocene(III): The Deceptive Simplicity of a Color Change

Abstract

Reduction of red Cp 2 TiCl 2 (Cp = cyclopentadienyl) with zinc dust in acetonitrile produces a blue solution of [Cp 2 Ti(NCMe) 2 ] +, which when exposed to air rapidly discolors to bright yellow. This behavior makes the blue solution a handy visual indicator for the presence of oxygen, but the chemistry is considerably more complicated than the primary colors suggest at first glance. Real-time mass spectrometric and colorimetric analysis reveals that oxidation from Ti(III) to Ti(IV) produces a host of oxygen-containing complexes, whose appearance parallels the observed color changes.