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

Treatment of OsCl 2 (PPh 3 ) 3 with HC≡CAr (Ar = Ph, p -tolyl) produced the η 3 -allenylcarbene complexes OsCl 2 (═CAr-η 2 -CH═C═CHAr)(PPh 3 ) 2 . Reactions of the η 3 -allenylcarbene complexes with gold alkynyls Au(C≡CR)(PPh 3 ) (R = Ph, p -tolyl, TMS, n Bu, CH(OEt) 2 ) or copper(I) alkynyls Cu(C≡CR) (R = Ph, TMS) in the presence of HNEt 3 Cl produced the osmabenzynes Os{≡CC(R)═C(CH 2 Ar)CH═CAr}Cl 2 (PPh 3 ) 2 . Computational studies suggest that the osmabenzynes are formed through electrocyclization of osmium alkynyl-allenylcarbene intermediates followed by protonation with HNEt 3 Cl.