An Electrophilic, Intramolecularly Base-Stabilized Platinum–Antimony Complex

As part of our interest in the chemistry of late transition metal complexes bearing cationic antimony ligands, we have investigated the reaction of ((o-(Ph₂P)­C₆H₄)₃)­SbClPtCl (1) with H₂O₂ and found that it affords [((o-(Ph₂P)­C₆H₄)₂(o-Ph₂PO)­C₆H₄)­SbPtCl]⁺ ([2–Cl]⁺), a monocationic complex with the newly installed P=O moiety coordinated intramolecularly to the antimony atom via a P=O → Sb dative bond. The Pt–Cl bond of this complex is readily activated by addition of a ligand such as cyclohexyl isocyanide. When carried out in the presence of AgBF₄, this reaction affords the dicationic complex [((o-(Ph₂P)­C₆H₄)₂(o-Ph₂PO)­C₆H₄)­SbPt­(CNCy)]⁺ ([2–CNCy]²⁺). In addition to structurally characterizing [2–Cl]⁺ and [2–CNCy]²⁺ as their chloride and tetrafluoroborate salts, respectively, we have also studied the reaction of [2–Cl]⁺ with AgBF₄ in the presence of PhCCH as a substrate surrogate. When monitored by ³¹P NMR spectroscopy in CDCl₃, this reaction shows the formation of a new species tentatively assigned to [((o-(Ph₂P)­C₆H₄)₂(o-Ph₂PO)­C₆H₄)­SbPt]²⁺ ([2]²⁺) stabilized by coordination of the alkyne. This formulation is supported by the elevated carbophilic reactivity of [2]²⁺, which readily catalyzes the cyclization of 2-allyl-2-(2-propynyl)­malonate. Altogether, these results show that the accumulation of charge in such reactive complexes can be facilitated by the intramolecular base-stabilization of the dinuclear core.