Intramolecular Hydride Migration Enables Ring Substitution in a Diphosphacyclobutadienyl Complex

While substitution reactions at coordinated carbocyclic π-ligands are well established, similar examples of direct substitution at the ring carbon atoms of mixed carbon-phosphorus π-systems have remained scarce, owing to the intrinsic bias towards P-centered reactivity. Herein, we report a hydride-for-phosphonium substitution at a coordinated phosphorus heterocyclic π-system: protonation of the complex [W(CO)3{η 4-(PPh3)2C2P2}] bearing a zwitterionic diphosphacyclobutadienyl ligand affords a tungsten hydride complex which undergoes a selective rearrangement to [W(CO)3(PPh3){η 4-(PPh3)HC2P2}][OTf] upon dissolution in acetonitrile. A combined experimental and computational investigation reveals a multistep pathway, in which a tungsten-mediated intramolecular hydride migration serves as the key step. Acetonitrile plays a crucial role in driving the reaction by stabilizing the coordinatively unsaturated intermediate generated upon hydride migration. Remarkably, despite its negative charge, the resulting phosphonium-hydro-diphosphete-diide ligand combines strong π-donor and pronounced π-acceptor properties, resulting in stronger binding to the tungsten carbonyl fragment than the cyclopentadienyl ligand, as evidenced by EDANOCV calculations and IR spectroscopy.