Preparation of Osmium η3‑Allenylcarbene Complexes and Their Uses for the Syntheses of Osmabenzyne Complexes

Treatment of OsCl2(PPh3)3 with HCCAr (Ar = Ph, p-tolyl) produced the η3-allenylcarbene complexes OsCl2(CAr-η2-CHCCHAr)­(PPh3)2. Reactions of the η3-allenylcarbene complexes with gold alkynyls Au­(CCR)­(PPh3) (R = Ph, p-tolyl, TMS, nBu, CH­(OEt)2) or copper­(I) alkynyls Cu­(CCR) (R = Ph, TMS) in the presence of HNEt3Cl produced the osmabenzynes Os­{CC­(R)C­(CH2Ar)­CHCAr}­Cl2(PPh3)2. Computational studies suggest that the osmabenzynes are formed through electrocyclization of osmium alkynyl-allenylcarbene intermediates followed by protonation with HNEt3Cl.