New PNHN Pincer-Type Ligands and Their Complexes for Transfer Hydrogenation

Abstract

The ligand tBu2PC2H4NHCH2Py (PNHN) was synthesized starting from 2-pyridinecarboxaldehyde and 2-chloroethanamine. Initial attempts for coordination of the PNHN ligand to a metal center was performed using [IrCl(COE)2]2, IrCl3·3H2O, [RuCl2(p-cymene)]2 and RuCl2(PPh3)3. The reaction between the PNHN ligand and [IrCl(COE)2]2 under H2 resulted in the chloride IrCl(H)2(PNHN). Synthesis of the active hydride species is currently under investigation. A reaction of the PNHN ligand with RuCl2(PPh3)3 under nitrogen afforded the dichloride RuCl2(PPh3)(PNHN). Treatment of the dichloride with KOBut in 2-pentanol led to the formation of the dihydride RuH2(PPh3)(PNHN). Formation of the 16-electron amido complex RuH(PPh3)3(PNN) was achieved through the evolution of H2. The dihydride demonstrated good potential catalytic activity for transfer hydrogenation of acetophenone and cyclohexanone. Current work involves the synthesis of a chiral analogue of the PNHN ligand.