An Antimony(V) Dication as a Z-Type Ligand: Turning on Styrene Activation at Gold

With the intent to demonstrate that the charge of Z-type ligands can be used to modulate the electrophilic character and catalytic properties of coordinated transition metals, we are now targeting complexes bearing polycationic antimony-based Z-type ligands. Toward this end, the dangling phosphine arm of ((o-(Ph2P)C6H4)(3))SbCl2AuCl (1) was oxidized with hydrogen peroxide to afford [((o-(Ph2P)C6H4)(2)(o-Ph2PO)C6H4)SbAuCl2](+) ([2 a](+)) which was readily converted into the dicationic complex [((o-(Ph2P)C6H4)(2)(o-Ph2PO)C6H4)SbAuCl](2+) ([3](2+)) by treatment with 2 equiv AgNTf2. Both experimental and computational results show that [3](2+) possess a strong Au -> Sb interaction reinforced by the dicationic character of the antimony center. The gold-bound chloride anion of [3](2+) is rather inert and necessitates the addition of excess AgNTf2 to undergo activation. The activated complex, referred to as [4](2+) [((o-(Ph2P)C6H4)(2)(o-Ph2PO)C6H4)SbAuNTf2](2+) readily catalyzes both the polymerization and the hydroamination of styrene. This atypical reactivity underscores the strong sigma-accepting properties of the dicationic antimony ligand and its activating impact on the gold center.