Reactions of Thianthrene and 10-Phenylphenothiazine with the Lewis Acids─Titanium Tetrachloride, Titanium Tetrabromide, Tin(IV) Tetrachloride, or Antimony(V) Pentachloride: The Competition between Coordination and Oxidation

Abstract

The oxidation of thianthrene and 10-phenylphenothiazine into cation radicals has been examined using redox-active Lewis acids. The reaction of titanium(IV) tetrachloride with thianthrene in toluene produces a solution with an EPR spectrum indicative of oxidation of thianthrene to a cation radical, but the molecular compound (1) (μ-thianthrene)Ti 2 (μ-Cl 2 )Cl 6 crystallized exclusively. Red crystalline (2) (μ-thianthrene)Ti 2 (μ-Br 2 )Br 6 formed similarly from titanium(IV) tetrabromide. In contrast, the reaction of antimony(V) pentachloride with thianthrene in toluene yielded crystalline (3) (thianthrene) • (SbCl 3 ), while the same reaction in acetonitrile produced crystals of (4) (thianthrene •+ )(SbCl 6 − ). The two paramagnetic salts differ in that in (3), the folded (thianthrene •+ ) cation radicals self-associate, whereas in (4), the (thianthrene •+ ) cation radicals are isolated from one another and are planar. The reaction of 10-phenylphenothiazine with titanium(IV) tetrachloride in toluene solution resulted in the formation of crystalline paramagnetic (5) (10-phenylphenothiazine •+ )-(Ti(μ-Cl) 3 Cl 6 − ) and the reaction of 10-phenylphenothiazine with tin(IV) tetrachloride produced paramagnetic (6) (10phenylphenothiazine •+ )(SnCl 5 − ).