Heterometallic Mg−Ba Hydride Clusters in Hydrogenation Catalysis

Abstract

Reaction of a MgN" 2 /BaN" 2 mixture (N" = N(SiMe 3 ) 2 ) with PhSiH 3 gave three unique heterometallic Mg/Ba hydride clusters: Mg 5 Ba 4 H 11 N" 7 • (benzene) 2 (1), Mg 4 Ba 7 H 13 N" 9 • (toluene) 2 (2) and Mg 7 Ba 12 H 26 N" 12 (3). Product formation is controlled by the Mg/ Ba ratio and temperature. Crystal structures are described. While 3 is fully insoluble, clusters 1 and 2 retain their structures in aromatic solvents. DFT calculations and AIM analyses indicate highly ionic bonding with MgÀ H and BaÀ H bond paths. Also unusual H À •••H À bond paths are observed. Catalytic hydrogenation with MgN" 2 , BaN" 2 and the mixture MgN" 2 /BaN" 2 has been studied. Whereas MgN" 2 is only active in imine hydrogenation, alkene and alkyne hydrogenation needs the presence of Ba. The catalytic activity of the MgN" 2 /BaN" 2 mixture lies in general between that of its individual components and strong cooperative effects are not evident.

In Situ Generation of Magnesium‐ and Calcium‐Based Grignard Reagents for Amide Synthesis

“…The heterobimetallic magnesium calciate crystallizes as [(hmds)Ca( μ ‐hmds) 2 Mg(hmds)] [9d] . Treating a 1 : 1 mixture of Mg(hmds) 2 and Ba(hmds) 2 with PhSiH 3 allows the isolation of an amide‐containing mixed metal hydride (Mg 5 Ba 4 H 11 (hmds) 7 ) [40] …”

“…[9d] Treating a 1 : 1 mixture of Mg(hmds) 2 and Ba(hmds) 2 with PhSiH 3 allows the isolation of an amidecontaining mixed metal hydride (Mg 5 Ba 4 H 11 (hmds) 7 ). [40]…”

Catalytic Main‐Group Metal Complexes of Phosphine‐Based Pincer Ligands

“…An internal alkene could also be hydrogenated under more forcing conditions, giving the alkane in 70 % yield. Only a handful of other magnesium complexes are known to catalyze alkene hydrogenation reactions [69–72] …”

Designing New Magnesium Pincer Complexes for Catalytic Hydrogenation of Imines and N-Heteroarenes: H2 and N–H Activation by Metal–Ligand Cooperation as Key Steps

“…In addition, cationic β-diketiminate aluminum complexes were found to be efficient catalysts in the hydrogenation of imines . Several heterobimetallic systems also exhibited capability in activation of H 2 and efficiency in hydrogenation of alkenes and imines . Very recently, magnesium pincer complex-catalyzed semihydrogenation of alkynes and hydrogenation of alkenes were reported by our group .…”

“…Catalytic hydrogenation of unsaturated molecules by H 2 is one of the most practical transformations in laboratory and industry . Classic catalysts mainly rely on late transition metals due to their efficiency in the cleavage of H 2 . , Due to the toxic and costly characteristics, it is increasingly interesting to use cheaper and more environmentally benign catalysts, such as the first-row transition metal compounds and frustrated Lewis pairs (FLPs). − However, as another large group of elements in the periodic table, the main-group metals have received much less attention in catalytic hydrogenation due to their lack of partially filled d orbitals and the instability of many main-group metal compounds, which largely impeded their application in bond activation. − In the 1960s, simple metal hydrides and inorganic bases were known as catalysts for the hydrogenation of benzophenone, alkenes, and alkynes, but harsh conditions were required . In 2008, Harder and co-workers reported a β-diketiminate calcium hydride complex and K, Ca, and Sr benzyl catalysts, providing relatively mild conditions for the catalytic hydrogenation of conjugated alkenes (Figure a) .…”