Metallic Barium: A Versatile and Efficient Hydrogenation Catalyst.

ABSTRACT: Ba metal was activated by evaporation and cocondensation with heptane. This black powder is a highly active hydrogenation catalyst for the reduction of a variety of unactivated (non-conjugated) mono-, di- and tri-substituted alkenes, tetraphenylethylene, benzene, a number of polycyclic aromatic hydrocarbons, aldimines, ketimines and various pyridines. The performance of metallic Ba in hydrogenation catalysis tops that of the hitherto most active molecular group 2 metal catalysts. Depending on the substrate, two different catalytic cycles are proposed. A: a classical metal hydride cycle and B: the Ba metal cycle. The latter is proposed for substrates that are easily reduced by Ba⁰ , that is, conjugated alkenes, alkynes, annulated rings, imines and pyridines. In addition, a mechanism in which Ba⁰ and BaH₂ are both essential is discussed. DFT calculations on benzene hydrogenation with a simple model system (Ba/BaH₂ ) confirm that the presence of metallic Ba has an accelerating effect.

SUBMITTER: Stegner P 

PROVIDER: S-EPMC7898525 | biostudies-literature | 2021 Feb

REPOSITORIES: biostudies-literature