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.