Cyclic Organoalanes

Cyclic Organoalanes

Author: Chemistry – A European Journal

Molecular main-group hydrides are interesting research targets with applications, e.g., in organic synthesis or as potential hydrogen storage materials. For example, a variety of four-coordinated monomeric aluminium hydrides stabilized by nitrogen donor Lewis bases have been isolated. N-heterocyclic carbenes (NHCs) are potent Lewis bases, and can also be employed to access aluminium hydride compounds.

Rajendra Ghadwal and colleagues, University of Bielefeld, Germany, have prepared the first carbocyclic aluminium hydrides [(ADC)AlH2]2 (general structure pictured) based on anionic dicarbenes (ADCs). The desired aluminium dihydrides were synthesized by reacting the respective anionic dicarbenes Li(ADCAr) with LiAlH4 (pictured below). The products are highly soluble in organic solvents and thermally stable. ADCs are stronger bases than NHCs. Thus, compounds of the type [(ADC)AlH2]2 can readily hydroaluminate CO2 at room temperature to give the formates [(ADC)Al(OCH(O))2]2 (pictured below on the right).



[(ADC)AlH2]2 could have applications in organic synthesis or in the catalytic reduction of carbon dioxide into value-added molecules. The products could also serve as starting materials for the preparation of unsaturated heterocycles with low-valent aluminium atoms.


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