Rational Design of a Well‐Defined Soluble Calcium Hydride Complex

Abstract

There is a wealth of information on transition-metal hydride complexes, a field driven by numerous applications in catalytic processes.[1] Recently, significant progress has also been made in the syntheses of lanthanide hydride complexes.[2] The area of main-group metal hydride complexes is biased in the sense that p-block metal hydrides are much better documented [3] than s-block metal hydrides, for which only few examples have been reported. [4] There are two important reasons for this imbalance: 1) relatively small bond energies in these predominantly ionic complexes allow for facile ligand exchange and thus formation of ligand-free metal hydride (this holds especially for the larger metals) and 2) very high lattice energies for early-main-group metal hydrides result in immediate precipitation of [MH x ] 1 . Consequently, the few examples of early-main-group metal hydrides all show the hydride encapsulated in mixed aggregates. A well-defined Li-Al-hydride [4a] cluster, a lithium amide-hydride aggregate [4b,c] and the alkoxide-hydride cluster (tBuOLi) 16 (LiH) 17 [4d] have been described. A magnesium hydride was found in an "inverse crown ether", that is, encapsulated in a ring that also contains metal ions (1).

Molecular Calcium Hydride: Dicalcium Trihydride Cation Stabilized by a Neutral NNNN‐Type Macrocyclic Ligand

“…[9] Ad issociated complex B [20] may also be formed (Scheme 3). Deuterium is activated either by the Lewis acidic calcium center in A or by s-bond metathesis in complex B to give the neutral dicalcium monodeuteride trihydride C under release of DSiPh 3 .T he silane DSiPh 3 [3,5] B(C 6 F 5 ) 3 catalyzed hydrogenation (4 atm of H 2 )of1,1'-DPE showed full conversion at 50 8 8Cafter 48 h, [21] whereas B(C 6 F 5 ) 3 -catalyzed transfer hydrogenation of 1,1'-DPE was complete at 25 8 8Ca fter 8h. [22] Thet ransfer hydrogenation of 1,1'-DPE catalyzed by ac ationic NHC gallium chloride at 20 8 8Cs howed 67 %conversion after 1h.…”

Reduction of Ketones with Hydrocarbon‐Soluble Calcium Hydride: Stoichiometric Reactions and Catalytic Hydrosilylation

“…[1] This dimeric complex, which readily dissolves in hydrocarbons like benzene, is stabilized towards ligand exchange and concomitant precipitation of insoluble CaH 2 by the bulky β-diketiminate ligand.…”

“…We recently published a synthetic route and crystal structure for the first well-defined calcium hydride complex (1) [Equation (1)]. [1] This dimeric complex, which readily dissolves in hydrocarbons like benzene, is stabilized towards ligand exchange and concomitant precipitation of insoluble CaH 2 by the bulky β-diketiminate ligand.…”

A Record‐Breaking Magnesium Hydride Molecular Cluster: Implications for Hydrogen Storage

“…[5] Secondly, following deprotonative magnesiation of PARA-H 2 by dibutylmagnesium to form PARA-(MgBu) 2 , they transformed the MgÀBu bonds into MgÀH bonds by addition of phenylsilane, PhSiH 3 . The hydride-carrying aptitude of PhSiH 3 had been demonstrated previously by Harder and co-workers, [6] and Jones and co-workers [7] in the respective formation of binuclear calcium and magnesium hydride complexes supported by mono b-diketiminate ligands; while Hill and co-workers [8] exploited it subsequently to build a larger tetranuclear magnesium amide-hydride cluster [Mg 4 H 6 (HMDS) 2 HMDS is 1,1,1,3,3,3 ). This extra MgH 2 appears to be an artefact of using excess MgBu 2 in the reaction which converts to MgH 2 on contacting the silane.…”