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Metallic Barium: A Versatile and Efficient Hydrogenation Catalyst
Author(s) -
Stegner Philipp,
Färber Christian,
Zenneck Ulrich,
Knüpfer Christian,
Eyselein Jonathan,
Wiesinger Michael,
Harder Sjoerd
Publication year - 2021
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202014326
Subject(s) - catalysis , chemistry , metal , benzene , conjugated system , organic chemistry , photochemistry , polymer
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 Ba 0 , that is, conjugated alkenes, alkynes, annulated rings, imines and pyridines. In addition, a mechanism in which Ba 0 and BaH 2 are both essential is discussed. DFT calculations on benzene hydrogenation with a simple model system (Ba/BaH 2 ) confirm that the presence of metallic Ba has an accelerating effect.