Molecular hydrides of alkaline earth metals supported by azamacrocycles

Abstract In contrast to heterogeneous catalysts used for industrial conversion of feedstock molecules, soluble homogeneous catalysts offer the opportunity to study elementary steps at the molecular level. In particular, the design of supporting ligands is crucial for the control of the central metal's properties. For late transition and precious metals, phosphines and N-heterocyclic carbenes were introduced to generate reactive and stereochemically defined sites. In contrast, suitable ancillary ligands for larger, more electropositive metals of the s-, p-, d-, and f-block are more difficult to design. We have introduced the neutral macrocyclic NNNN-type tetraamine ligand Me4TACD based on cyclen (1,4,7,10-tetraazacyclododecane or [12]aneN4) to solubilize insoluble solid-state hydrides, currently of interest as hydrogen storage materials. A series of cationic molecular hydrides [(Me4TACD)MH]+ (M = Mg - Ba) has been prepared, characterized, and tested for their activity to catalyze H2/D2 isotopic exchange, olefin hydrogenation, and hydrofunctionalization.