Syntheses and Theoretical and Mechanistic Aspects of 1-Thia-2,4- and 1-Thia-3,4-diphosphole Formed from CS2 and tBuCP and Crystal and Molecular Structure of the First 1-Thia-3,4-diphosphole Complex:  cis-[{PtCl2(PEt3)}2(P2SC2 tBu2)]

The reaction of tBuCP with CS2 (or its ylide type complexes such as R3PCS2 (R = Et, Ph, cyclohexyl), (C5H10N)2CCS2, or (C4H8NO)2CCS2) gives a mixture of 3,5-di-tert-butyl-1-thia-2,4-diphosphole and 2,5-di-tert-butyl-1-thia-3,4-diphosphole, which were characterized by NMR spectroscopy. The latter was also characterized by the single-crystal X-ray structure determination of its bis(platinum(II)) complex [(PtCl2PEt3)2(μ-P2SC2 tBu2)]. This is the first structural characterization of a 1-thia-3,4-diphosphole ring. The mechanism of these reactions was explored by B3LYP/6-311+G** level quantum chemical calculations. The reaction pathway involves a phosphadithiolediylcarbene and its diphosphatetrathiafulvalene dimer as intermediates. Several other possible reaction pathways were ruled out.