Unexpected Thermal Reactivity of Phosphirano‐[1,2]thiaphosphole P –W(CO) 5 Complexes

Spiro[fluorene‐9,6′‐[2]thia[1]phosphabicyclo[3.1.0]hex[3]enes] 7a – c have been obtained in one step from 3,5‐diaryl‐1,2‐thiaphospholes and 9‐diazofluorene or its 2,7‐dibromo derivative. The bicyclic phosphiranes are stable against water and resist attempts at sulfuration or selenation of the phosphorus atom. However, cleavage of the P–C ring fusion with hydrogen chloride followed by hydrolysis led to the monocyclic 2‐(9 H ‐fluoren‐9‐yl)‐2,3‐dihydro‐1,2‐thiaphosphole 2‐oxides 8a – c . Phosphiranes 7a – c also react to form the hexacarbonyltungsten‐( P – W ) complexes 10a – c readily and in high yields. These complexes rearrange in toluene solution at 50–80 °C to form the spiro[fluorene‐9,2′‐[1]phospha[6]thiabicyclo[3.1.0]hex‐3‐ene]‐W(CO) 5 ‐( P – W ) complexes 11a – c , which are the first representatives of ring‐fused thiaphosphiranes. Compound 11a is readily desulfurated with tributylphosphane to form the highly oxygen‐sensitive spiro[fluorene‐9,2′‐[2 H ]phosphole] 13 , which is reconverted into 11a upon treatment with sulfur. Bicyclic 1,3,2‐dithiaphospholanes 12a – c are formed as minor byproducts of the thermal isomerization of phosphiranes 10 . Compound 10a slowly rearranges in solution to give 12a as the sole product. Compounds 12 may result from a formal [3+2] cycloaddition reaction of an α,β‐unsaturated thione, formed by partial decomposition of 10 , with a dipolar valence isomer of 10 or 11 , featuring aW(CO) 5 ‐complexed thiocarbonyl‐phospha‐ylide dipole (R 2 C=S + –P – R). W(CO) 5 complexation is not a prerequisite for the cycloaddition reaction: the uncomplexed phosphirano‐thiaphosphole 7a reacts with thiobenzophenone in the same way to form the bicyclic 1,3,2‐dithiaphospholane 18 in high yield. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)