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-(Ph2 P)C6 H4 )3 )SbCl2 AuCl (1) was oxidized with hydrogen peroxide to afford [((o-(Ph2 P)C6 H4 )2 (o-Ph2 PO)C6 H4 )SbAuCl2 ]+ ([2 a]+ ) which was readily converted into the dicationic complex [((o-(Ph2 P)C6 H4 )2 (o-Ph2 PO)C6 H4 )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-(Ph2 P)C6 H4 )2 (o-Ph2 PO)C6 H4 )SbAuNTf2 ]2+ readily catalyzes both the polymerization and the hydroamination of styrene. This atypical reactivity underscores the strong σ-accepting properties of the dicationic antimony ligand and its activating impact on the gold center.