Metal-Ligand Role Reversal: Hydride-Transfer Catalysis by a Functional Phosphorus Ligand with a Spectator Metal.

Hydride transfer catalysis is shown to be enabled by the nonspectator reactivity of a transition metal-bound low-symmetry tricoordinate phosphorus ligand. Complex ·[Ru], comprising a nontrigonal phosphorus chelate (, P(N(-N(2-pyridyl)CH)) and an inert metal fragment ([Ru] = (MeC)Ru), reacts with NaBH to give a metallohydridophosphorane (·[Ru]) by P-H bond formation. Complex ·[Ru] is revealed to be a potent hydride donor (Δ° < 41 kcal/mol, Δ° = 38 ± 2 kcal/mol in MeCN). Taken together, the reactivity of the ·[Ru]/·[Ru] pair comprises a catalytic couple, enabling catalytic hydrodechlorination in which phosphorus is the sole reactive site of hydride transfer.