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 P-31 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.