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)C 6 H 4 ) 2 ) and an inert metal fragment ([Ru] = (Me 5 C 5 )Ru), reacts with NaBH 4 to give a metallohydridophosphorane ( 1 H ·[Ru]) by P-H bond formation. Complex 1 H ·[Ru] is revealed to be a potent hydride donor (Δ G ° H-,exp < 41 kcal/mol, Δ G ° 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.