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 1·[Ru]+, comprising a nontrigonal phosphorus chelate (1, P­(N­(o-N­(2-pyridyl)­C6H4)2) and an inert metal fragment ([Ru] = (Me5C5)­Ru), reacts with NaBH4 to give a metallohydridophosphorane (1 H ·[Ru]) by P–H bond formation. Complex 1 H ·[Ru] is revealed to be a potent hydride donor (ΔG°H–,exp < 41 kcal/mol, ΔG°H–,calc = 38 ± 2 kcal/mol in MeCN). Taken together, the reactivity of the 1·[Ru]+/1 H ·[Ru] pair comprises a catalytic couple, enabling catalytic hydrodechlorination in which phosphorus is the sole reactive site of hydride transfer.