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

Abstract

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 H(2)/KOH results in H(2) 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.

Synthesis of Peptides and Pyrazines from β‐Amino Alcohols through Extrusion of H2 Catalyzed by Ruthenium Pincer Complexes: Ligand‐Controlled Selectivity

“…[16] For example, the PNN Ru II pincer complex 1 (Scheme 1) catalyzes the direct synthesis of amides from alcohols and amines with liberation of H 2 [17] (Scheme 2, Eq. (1)).…”

Bond Activation by Metal-Ligand Cooperation: Design of “Green” Catalytic Reactions Based on Aromatization-Dearomatization of Pincer Complexes

“…12). We believe that upon reaction of alkoxide 19 with ammonia, the hydride on the ruthenium is transferred to C9 center of acridine to form the intermediate 20, as we have observed with the analogous chloride (instead of alkoxide) complex [79]. Presumably, de-coordination of the acridine nitrogen followed by NH 3 coordination positions the acridine ring favorably for hydride transfer.…”

“…The selectivity for the linear primary amines is improved by the use of co-solvents such as toluene or dioxane in water. While insufficient mechanistic data exist at present for the direct amination reaction, ongoing studies in our lab suggests the involvement of acridine middle aryl ring (C9) as a cooperative site in synergy with the metal center (reaction of complex 16 with ammonia, either in the presence or absence of alcohol, led to a new complex resulting from hydride transfer to C9; its structure (C9 being CH 2 ) was solved by an X-ray diffraction study [79]) (Fig. 12).…”

Cleavage of the βO4 linkage of lignin using group 8 pincer complexes: A DFT study

“…The catalysis results in R H and ROSiEt 3 . On the other hand, some pincer complexes have been shown to have the ability to catalyze hydrogen transfer and hydrogenation reactions [34,35]. Gunanathan et al have studied the H 2 activation and hydride transfer using a PNP type Ru carbonyl complex via both experimental and computational approaches.…”