Molecular Magnesium Hydrides

Abstract

Solid magnesium hydride [MgH ] has been pursued as a potential hydrogen-storage material. Organic chemists were rather interested in soluble magnesium hydride reagents from mid-20th century. It was only in the last two decades that molecular magnesium hydride chemistry received a major boost from organometallic chemists with a series of structurally well-characterized examples that continues to build a whole new class of compounds. More than 40 such species have been isolated, ranging from mononuclear terminal hydrides to large hydride clusters with more than 10 magnesium atoms. They provide not only insights into the structure and bonding of Mg-H motifs, but also serve as models for hydrogen-storage materials. Some of them are also recognized to participate in catalytic transformations, such as hydroelementation. Herein, an overview of these molecular magnesium hydrides is given, focusing on their synthesis and structural characterization.

Zinc Dihydride and Mixed Halo Hydrides Supported by an N‐Heterocyclic Carbene

“…Reaction with iodine follows a similar redox pathway to provide 1c along with H 2 liberation. This redox property may be of interest considering the potential use of molecular metal hydrides as model compounds for hydrogen‐storage materials …”

Super‐Bulky Penta‐arylcyclopentadienyl Ligands: Isolation of the Full Range of Half‐Sandwich Heavy Alkaline‐Earth Metal Hydrides

“…The lighter magnesium hydride complexes are also regarded as potential materials for hydrogen storage . Among the limited number of well‐defined molecular Group 2 metal–hydride complexes, magnesium hydrides dominate with over 40 examples . Only a handful of calcium hydrides are known .…”

“…[4] Among the limited number of welldefined molecular Group 2m etal-hydride complexes,m agnesium hydrides dominate with over 40 examples. [5] Only ah andful of calcium hydrides are known. [6] Theh eavier strontium and barium hydrides are scarce,w ith ar ecord of three [7] and two [8] respectively.T he tapering distribution is consistent with the increasing difficulty in isolating Group 2 metal hydride species (Mg < Ca < Sr < Ba), mainly attributed to the increasing ionic character and bond lengths,a nd decreasing bond energies as the group is descended.…”

A Hexagonal Planar Metal Complex

“…Moreover, the formation of direct bonds between transition metals and s‐block metals is quite unique and will further enrich the area of heterometallic complexes . As both of the Group 10 metals Ni and Pd are well known to activate dihydrogen under mild conditions and MgH 2 is being tested as a hydrogen‐storage material, new interesting applications with impact for catalytic dihydrogen activation can be expected for these complexes.…”