Formation of 5-phenyl-1,2-dithiole-3-thione from molybdenum dithiopropiolato complexes

Molybdenum dithiopropiolato complexes, [(η5-C5R4R′)Mo(CO)2(η2-S2CCCPh)] (R=H, R′=Me 1a, R=R′=H 1b; R=R′=Me 1c) react with trimethylamine-N-oxide (TMNO · 2H2O) under mild thermolysis to form 5-phenyl-1,2-dithiole-3-thione (2). The reaction proceeds through the formation of the oxo-complexes, [(η5-C5R4R′)Mo(O)(η3-S2CCCPh)] (R=H, R′=Me 3a, R=R′=H 3b; R=R′=Me 3c). Direct reaction of 3a–c with TMNO · 2H2O under thermolysis also results in formation of 2.