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.

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 · + ) 2 (Sb 2 (μ-Cl) 2 Cl 6 2- ) · (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 ) (10-phenylphenothiazine · + )(SnCl 5 - ).