Alkali Metal Hydride Complexes: Well-Defined Molecular Species of Saline Hydrides

Abstract

The first examples of well-defined alkali metal hydride complexes have been synthesised and characterised in recent years, and their properties and underlying principles for their generation and stabilisation are emerging. This article gives an account of the hydrides of the alkali metals (Group 1 metals) and selected '-ate' complexes containing hydrides and alkali metals, and reviews the chemistry of well-defined alkali metal hydride complexes including their syntheses, structures, and characteristics. The properties of the alkali metal hydrides LiH, NaH, KH, RbH, and CsH are dominated by their ionic NaCl structure. Stable, soluble, and well-defined LiH and NaH complexes have been obtained by metathesis and b-hydride elimination reactions that require suitable ligands with some steric bulk and the ability to coordinate to several metal ions. These novel hydride complexes reward with higher reactivity and different properties compared with their parent ionic solids.

Ring‐Shaped Phosphinoamido‐Magnesium‐Hydride Complexes: Syntheses, Structures, Reactivity, and Catalysis

“…Of the binary hydrogen compounds of the chemical elements, s‐block metal hydrides are unique due to the highly electropositive nature of the alkali and alkaline earth metals, and their electronegativity difference from hydrogen. Thus, these metal hydrides are generally classified as ionic or saline . Furthermore, the s‐block is home to highly earth‐abundant, non‐toxic and even biocompatible metals such as Na, K, Mg and Ca, all of which offer a range of properties for future sustainable chemical applications .…”

“…A range of well‐defined s‐block metal–hydride complexes have been reported in very recent years, and these have already been successfully used in stoichiometric and catalytic transformations. In addition, the hydrogen storage properties of some of these examples have been investigated . The recent success in this area can be attributed to both the development of suitable synthetic strategies to generate s‐block metal–hydride fragments, and the design and use of stabilising ligand systems that prevent dismutation and other decomposition reactions of the formed complexes, leading to the precipitation of insoluble saline metal hydrides.…”

“…Thus, these metal hydrides are generally classified as ionic or saline. [2,3] Furthermore, the s-block is home to highly earth-abundant,n on-toxic and even biocompatible metals such as Na, K, Mg and Ca, all of which offer ar ange of properties for future sustainable chemical applications. [4] Ar ange of well-defined s-block metal-hydride complexes have been reported in very recent years, and these have already been successfully used in stoichiometric and catalytic transformations.…”

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

“…Molecular alkaline-earth-metal hydrides continue to receive growing interest, [1] as they are used as low-cost and non-toxic alternatives to transition-metal catalysts in various organic transformations. [2] Thel ighter magnesium hydride complexes [3] are also regarded as potential materials for hydrogen storage.…”

A Molecular Barium Hydrido Complex Stabilized by a Super‐Bulky Hydrotris(pyrazolyl)borate Ligand

“…There is currently intense interest in the synthesis and reactivity of Group 2m etal hydride complexes, [1] as they are low-cost and non-toxic alternatives to transition-metal catalysts in many organic transformations, [2] and they are also regarded as potential materials for hydrogen storage. [3] Despite their propensity,w ell-defined molecular Group 2 metal-hydride complexes are limited, especially for the heavy alkaline-earth metals (Ca, Sr, Ba).…”