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

Abstract

Reduction of red CpTiCl (Cp = cyclopentadienyl) with zinc dust in acetonitrile produces a blue solution of [CpTi(NCMe)], 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.

Shining Light on TiIV Complexes: Exceptional Tools for Metallaphotoredox Catalysis

“…[83,85,86] The presence of molecular oxygen is often detrimental for the stability of the Ti III species: when those are exposed to O 2 , solutions tend to be swiftly bleached to the corresponding yellow Ti IV derivatives. [87] Due to the rapid chloride ion dissociation, [88] the presence of H 2 O can lead to unsuccessful pinacol coupling reactions. On the other hand, water is a useful solvent for HATtype chemistry, [89] where Ti III complexes can drive the efficient reduction of carbon-centered radicals of diverse nature via a HAT process.…”

Gas-Phase Oxidation of Reactive Organometallic Ions

“…Preparation of [Cp2Ti(NCCH3)2] + was done using a previously published procedure. 16 40,41 A spin-polarized UPBE/DZP formalism was used in SIESTA, with Troullier-Martins norm-conserving pseudopotentials, and dispersive interactions included at the D2 level of Grimme, which is appropriate for gas -phase metal species. 42,43 The effects of Hartree-Fock exchange and basis set size were considered by using a series of unrestricted methods available in the ORCA software.…”

“…4 We have also studied the reaction of a reduced titanocene complex (which is used as an indicator for atmospheric oxygen) 15 with O2. 16 We wondered whether any of this chemistry might form the basis for sensitively detecting impurity problems associated with operation of the mass spectrometer, as opposed to solution contamination, where rigorous drying and deoxygenation protocols usually suffice. In this paper we focus on the use of reactive titanium and zirconium complexes as indicators for both gas phase oxygen, and in the latter case, also water.…”

Gas-Phase Oxidation of Reactive Organometallic Ions

“…Preparation of [Cp2Ti(NCCH3)2] + was done using a previously published procedure. 16 Cp2TiCl2 (32 mg, 0.…”

“…4 We have also studied the reaction of a reduced titanocene complex (which is used as an indicator for atmospheric oxygen) 15 with O2. 16 We wondered whether any of this chemistry might form the basis for sensitively detecting impurity problems associated with operation of the mass spectrometer, as opposed to solution contamination, where rigorous drying and deoxygenation protocols usually suffice. In this paper we focus on the use of reactive titanium and zirconium complexes as indicators for both gas phase oxygen, and in the latter case, also water.…”