Macrocyclic Ligands for Molecular Hydrides of s-Block Metals

Abstract

In organometallic chemistry and homogeneous catalysis, the design and development of ancillary ligands are pivotal in order to control the central metalʼs reactivity. Whilst for classical late transition and precious metals, phosphines and N-heterocyclic carbenes have been successfully introduced to generate reactive, and even stereochemically defined sites, the search for suitable ancillary ligands for larger, more electropositive metals of s-, p-, d-, and f-block is often more difficult. We have introduced NNNN-type macrocyclic ligands based on cyclen (1,4,7,10-tetraazacyclododecane or [12]aneN₄, viz. the amido triamine ligand Me₃TACD and the neutral tetraamine ligand Me₄TACD. Both ligands have been used to solubilize insoluble solid-state hydrides, currently of interest as hydrogen storage materials, to give molecular hydrides with interesting reactivity toward small molecules such as H₂ and CO₂.