“Long-Range” Metal−Ligand Cooperation in H₂ Activation and Ammonia-Promoted Hydride Transfer with a Ruthenium−Acridine Pincer Complex

The acridine-based pincer complex 1 exhibits an unprecedented mode of metal−ligand cooperation involving a “long-range” interaction between the distal acridine C9 position and the metal center. Reaction of 1 with H₂/KOH results in H₂ splitting between the Ru center and C9 with concomitant dearomatization of the acridine moiety. DFT calculations show that this process involves the formation of a Ru dihydride intermediate bearing a bent acridine ligand in which C9 is in close proximity to a hydride ligand followed by through-space hydride transfer. Ammonia induces transfer of a hydride from the Ru center of 1 to C9 of the flexible acridine pincer ligand, forming an unusual dearomatized fac-acridine PNP complex.