Transformations of Benzothiadiphosphole System: General One-Pot Synthesis of 1,2,5-Dithiaphosphepines and Their Precursor Phosphanethiols

Treatment, at room temperature, of benzothiadiphosphole 1 with BrMg(CH2)5MgBr gives intermediate A, which was allowed to stand for about 3 hat room temperature. The subsequent addition of RMgX to the reaction mixture and the final treatment with an excess of S8 and water affords the dithiaphosphepine sulfide 8 in good yields. The structure of this new heterocyclic system, containing both an S S unit and a P S group, is confirmed by an single crystal X-ray structure determination. If the reaction is carried out without final treatment with sulfur we obtain, using PhMgBr as mono-Grignard reagent, the corresponding ring-opened product 11b, which can be easily transformed into the corresponding ring-opened sulfide 12b by simple treatment with elemental sulfur. Further addition of sulfur to 12b gives quantitatively the cyclic dithiaphosphepine sulfide 8b. The two phosphanethiols 11b and 12b are of considerable interest. In fact, recently, attention has increasingly been paid to the coordination chemistry of polyden-tate ligands incorporating both thiolate and tertiary phosphine groups, also known as S P S pincer ligands.