A Hydrocarbon‐Soluble Lithium Hydride Complex

Abstract

Lithium hydride is the lightest metal hydride and is considered to be the simplest ionic compound. [1,2] With a low molecular weight of just under 8 g mol À1 and a relatively high hydrogen content of 12.7 % it is of interest for numerous applications including hydrogen storage technologies [3] and uses in organic and inorganic synthesis. [4] LiH crystallizes with a rock salt structure and shows a high lattice energy of approximately 220 kcal mol À1 . [1] This renders the material stable and relatively easy to handle, but also makes it too insoluble and unreactive for many applications.In recent years, a number of well-defined and structurally characterized molecular s-block metal hydride complexes have been forthcoming and show significant differences to the properties of the parent bulk metal hydride, that is, MH for the group 1 metals and MH 2 for the group 2 metals. The majority of these achievements concentrate on the molecular compounds of the group 2 metals Be, [5] Mg, [6] and Ca. [7] Some of these hydride complexes have already been employed in hydrometalation reactions [8] and have even been successfully used as a hydrogenation catalyst on alkenes. [9] The majority of hydride complexes involving group 1 metals are mixed metal systems, and can be considered ate complexes, for example LiAlH 4 and its derivatives. [2,10] Some remarkable examples include mixed metal systems such as [[{(Me 3 Si) 2 N}AlH 2 Li] 3 (LiH)] having a central distorted (LiH) 4 cube featuring one hydride moiety solely bound to Li cations. [11] There are also a number of complexes having an interstitial hydride surrounded by seven or eight lithium ions, as in cationic [L 6 HLi 8 ] + (L = a chelating monoanionic Nligand) and the related neutral complex [L 6 HLi 7 ]. [12,13] Active forms of alkali metal hydrides MH (M = Li, Na, K) have been obtained from mixtures of metal alkoxides and alkyl metal compounds in the presence or absence of dihydrogen or from alkyl metal compounds and silanes. [4,14] Mixed lithium alkoxide/lithium hydride aggregates have been generated thermally or photolytically in solution, [15] and the remarkable 'superaggregate' [(tBuOLi) 16 (LiH) 17 ] was, in one instance, obtained in an undetermined yield and structurally characterized. [16]

Well‐Defined, Nanometer‐Sized LiH Cluster Compounds Stabilized by Pyrazolate Ligands

“…The Li À N(pz) bond lengths in the characterized examples are in a similar range to previously reported examples of (pz)Li compounds. [15,16] The Li···H contacts measure around 2 and are close to those of previously characterized examples, [8][9][10][11][12] and to that in cubic Angewandte Chemie LiH (ca. 2.04 ).…”

“…However, product mixtures were formed across the investigated pz/hydride ratio range. The addition of THF to hydride-rich solutions reproducibly led to low to moderate yields of isolated [Li(thf) 4 ][(pz) 12 Li 37 -(thf) 2 H 26 ] (4; Scheme 1 and Figure 1). [14] The same complex 4 was obtained by recrystallizing a crude product rich in [(pz) 12 Li 37 H 25 ] (3) from THF/n-hexane.…”

“…[9,10] The structure of [(pz) 10 [14] and the salt [Li(thf) [14] are based on lattice cutout B (Figure 2 Figure S12). For the [(pz) 12 [14] which suggests that this is the most reactive site of the complex.…”

“…[11] We have recently used the silane method to synthesize hydrocarbon-soluble [(LLi) 4 (LiH) 4 ] (L= DipNPPh 2 , Dip = 2,6-iPr 2 C 6 H 3 ), which contains a central (LiH) 4 cube. [12] The complex was found to undergo hydrolithiation reactions with activated unsaturated organic substrates, [12,13] although the stabilizing phosphinoamide ligand L can perform competing addition reactions with the substrates. [13] Herein, we report the generation and structural characterization of a family of up to nanometersized, well-defined pyrazolato lithium hydride clusters from hydrocarbon solutions in a bottom-up approach.…”

Sensitive Approach for Voltammetric Determination of Carbendazim Based on the Use of an Anionic Surfactant

“…Furthermore, cationic [L 6 Li 8 H] + (L=chelating anionic ligand) and neutral [L 6 Li 7 H] complexes with an interstitial hydride ion have been prepared,9, 10 and the structure of the large mixed lithium alcoholate/hydride cluster [( t BuOLi) 16 (LiH) 17 ] was reported 11. We have recently used the silane method to synthesize hydrocarbon‐soluble [(LLi) 4 (LiH) 4 ] (L=DipNPPh 2 , Dip=2,6‐ i Pr 2 C 6 H 3 ), which contains a central (LiH) 4 cube 12. The complex was found to undergo hydrolithiation reactions with activated unsaturated organic substrates,12, 13 although the stabilizing phosphinoamide ligand L can perform competing addition reactions with the substrates 13.…”