Structural Evidence for Pnictogen-Centered Lewis Acidity in Cationic Platinum-Stibine Complexes Featuring Pendent Amino or Ammonium Groups

As part of our continuing interest in the chemistry of cationic antimony Lewis acids as ligands for late transition metals, we have now investigated the synthesis of platinum complexes featuring a triarylstibine ligand substituted by an o-(dimethylamino)methyl]phenyl group referred to as Ar^N. More specifically, we describe the synthesis of the amino stibine ligand Ph₂SbAr^N (L) and its platinum dichloride complex LPtCl]Cl which exists as a chloride salt and which shows weak coordination of the amino group to the antimony center. We also report the conversion of LPtCl]Cl into a tricationic complex LHPt(SMe₂)]³⁺ which has been isolated as a tris-triflate salt after reaction of LPtCl]Cl with SMe₂, HOTf and AgOTf. Finally, we show that LHPt(SMe₂)]OTf]₃ acts as a catalyst for the cyclization of 2-allyl-2-(2-propynyl)malonate.