Synthesis of Ru-PNPC Pincer Complexes and Applications in Catalytic Hydrogenation and Dehydrogenation Reactions

The reaction of N,N-bis(2-(diisopropylphosphaneyl)ethyl)prop-2-yn-1-amine 1 with [Ru(CO)ClH(PPh₃)₃] leads to the formation of a new class of cyclometallated PNPC pincer complexes. Several examples of this class of compounds are synthesized and characterized. They, specifically complexes 2 and 3, show good to excellent activity and selectivity in additive-free formic acid dehydrogenation, and transfer (de)hydrogenation reactions of different functional groups (ketone, alkyne, and alcohol). Theoretical and experimental studies reveal two competing pathways for the dehydrogenation of formic acid. The Ru-H pathway proceeds via the coordination site trans to the propylene arm of the ligand, whereas in the Ru-C pathway, a de-coordination of the propylene arm is observed.