Catalytic Acceptorless Dehydrogenation of Amines with Ru(P^R₂N^R′₂) and Ru(dppp) Complexes

Abstract

[Ru­(Cp)­(PPh 2NBn 2)­(MeCN)]­PF6 (1; PPh 2NBn 2 = 1,5-benzyl-3,7-phenyl-1,5-diaza-3,7-diphosphacyclooctane) and [Ru­(Cp)­(dppp)­(MeCN)]­PF6 (2; dppp = 1,3-bis­(diphenylphosphino)­propane) are both active toward the acceptorless dehydrogenation of benzylamine (BnNH2) and N-heterocycles. The two catalysts have similar activities but different selectivities for dehydrogenation products. Independent synthesis of a [Ru­(Cp)­(PPh 2NBn 2)­(NH2Bn)]­PF6 adduct (3) reveals the presence of a hydrogen bond between the bound amine and the pendent base of the PPh 2NBn 2 ligand. Preliminary mechanistic studies reveal that the benzylamine adduct is not an on-cycle catalyst intermediate.

Selective Acceptorless Dehydrogenation of Primary Amines to Imines by Core–Shell Cobalt Nanoparticles

“…Consequently, it would be advantageous to eliminate the use of oxidants for this process. Recently, the acceptorless dehydrogenation (AD) of primary amines to imines was shown to be an attractive method for their preparation as fewer side‐products are obtained under more inert conditions (with the release of H 2 ) . As this reaction is more thermodynamically challenging, the acceptorless dehydrogenation of primary amines has received less attention compared to that of N‐heterocycles, with the later reaction having been widely explored for hydrogen storage applications …”

“…Acceptorless dehydrogenation of primary amines is usually achieved with molecular catalysts mainly based on Ru . However, the aldimine intermediate may undergo a second dehydrogenation to afford a nitrile, which competes with imine formation via a transamination step, resulting in low selectivity of the desired imines.…”

“…However, the aldimine intermediate may undergo a second dehydrogenation to afford a nitrile, which competes with imine formation via a transamination step, resulting in low selectivity of the desired imines. For example, a Ru complex with a P, N‐ligand catalyzes the dehydrogenation of benzylamine to imines in only 54 % yield because of the formation of the nitrile product …”

Ruthenium Arene Complexes with α‐Aminoacidato Ligands: New Insights into Transfer Hydrogenation Reactions and Cytotoxic Behaviour

“…Ruthenium(II) arene compounds, bearing a typical three leg piano stool structure, have aroused a huge interest for their possible catalytic and biological applications In particular, they have been intensively investigated in the last decade as catalytic precursors for hydrogenation reactions, following the success encountered by the catalytic systems developed by Noyori (Figure a) and culminating with the Nobel Prize award . On the other hand, RAPTA compounds, incorporating the amphiphilic 1,3,5‐triaza‐7‐phosphaadamantane (pta) ligand (Figure b), and RAED compounds, containing a bidentate ethylenediamine ligand (Figure c), exhibit promising anticancer properties, that have stimulated the attention on many other analogous complexes.…”

Catalytic Ammonia Oxidation to Dinitrogen by Hydrogen Atom Abstraction

“…The molecular structure shows a three‐legged piano‐stool complex with a Ru‐NH 3 bond distance of 2.1790(16) Å, Figure . Intramolecular hydrogen bonding between the pendant NPh nitrogen atom and the NH 3 ligand is evident in the solid‐state structure, exhibiting a N1⋅⋅⋅N3 distance of 2.852 Å and a Ru‐NH 2 H⋅⋅⋅N Ph through‐space distance of 2.052 Å . Solution‐state NMR data of [Ru 15 NH 3 ] + containing 15 NPh groups indicate that the hydrogen bonding persists in solution (see SI for details).…”