Abstract
The catalytic dehydrocoupling of amine–boranes has recently received a great deal of attention due to its potential in hydrogen storage applications. The use of aluminum catalysts for this transformation would provide an additional cost-effective and sustainable approach towards the hydrogen economy. Herein, we report the use of both N-heterocyclic imine (NHI)- and carbene (NHC)-supported Al(III) hydrides and their role in the catalytic dehydrocoupling of Me2NHBH3. Differences in the σ-donating ability of the ligand class resulted in a more stable catalyst for NHI-Al(III) hydrides, whereas a deactivation pathway was found in the case of NHC-Al(III) hydrides.
Highlights
Main group chemistry has seen a resurgence of interest in recent years, driven by the need for more economically viable and eco-friendly processes
Use of p-block elements such as aluminum allows for the use of earth-abundant and environmentally benign elements, with aluminum being the third most abundant element in the
We propose that this new minor N-heterocyclic imine (NHI)-containing species is the first step in the catalytic cycle, whereupon σ-bond that this new minor NHI‐containing species is the first step in the catalytic cycle, whereupon σ‐bond metathesis of Al–H with the protic N–H bond of Me2 NHBH3 occurs to yield 1 eq of H2 and compound metathesis of Al–H with the protic N–H bond of Me2NHBH
Summary
Main group chemistry has seen a resurgence of interest in recent years, driven by the need for more economically viable and eco-friendly processes. Owing to their high stability and Lewis acidity, Al(III) catalysts in the form of trialkyl or trihalide derivatives have traditionally been used in Zieglar–Natta [1] and Friedel–Crafts [2] reactions, respectively. The chemistry of low-oxidation and/or coordinate Al complexes (and p-block complexes) is still in its infancy, and advances in past decades have shown that main group complexes can act as transition metals [3,4,5]. Few examples of low-oxidation and/or coordinate Al complexes in catalysis have been reported, such as the use of aluminum ions, R2 Al+ , in polymerization systems [6,7] and the recent example of dialumene—a compound with a neutral aluminum–aluminum double bond—for the catalytic reduction of CO2 [8]
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