A Stiboranyl Platinum Triflate Complex as an Electrophilic Catalyst

With the view of developing electrophilic late-transition-metal catalysts, we have now synthesized [(o-(Ph2P)­C6H4)2Sb­(OTf)2]­Pt­(OTf) (2) and [(o-(iPr2P)­C6H4)2Sb­(OTf)2]­Pt­(OTf) (4) by treatment of the corresponding trichlorides ([(o-(R2P)­C6H4)2SbCl2]­PtCl (R = Ph, iPr)) with 3 equiv of AgOTf. The crystal structures of 2 and 4 confirmed that the chloride ligands have been fully substituted by more labile triflate ligands. Despite structural similarities in the dinuclear cores of 2 and 4, only 2 acts as a potent carbophilic catalyst in enyne cyclization reactions. The high activity of 2 is also reflected by its ability to promote the addition of pyrrole and thiophene derivatives to alkynes. Structural and computational analyses suggest that the superior reactivity of 2 results from both favorable steric and electronic effects. Finally, a comparison of 2 with the previously reported self-activating catalyst [(o-(Ph2P)­C6H4)2Sb­(OTf)2]­PtCl underscores the benefits of triflate for chloride substitution.