A Cationic Barium Hydride Complex Supported by an NNNN-Type Macrocycle

Abstract

The dibenzyl complex of barium [(Me4TACD)Ba(CH2Ph)2] was prepared by reacting [Ba(CH2Ph)2] with NNNN-type macrocycle Me4TACD (Me4TACD=1,4,7,10-tetramethyltetraazacyclododecane) and isolated as yellow crystals. Single crystal X-ray diffraction revealed η2- and η3-coordination of the benzyl groups. The benzylbarium cation in [(Me4TACD)Ba(CH2Ph)(thf)][B(C6H3-3,5-Me2)4] was obtained upon protonolysis of the neutral bariumdibenzyl with the weak Brønsted acid [NEt3H][B(C6H3-3,5-Me2)4] and isolated as colorless crystals. When the benzylbarium cation was reacted with H2 (1 bar) in THF at room temperature, colorless crystals of the dinuclear hydride complex [(Me4TACD)2Ba2(μ-H)2(thf)4][B(C6H3-3,5-Me2)4]2 precipitated from the reaction mixture and characterized by single crystal X-ray diffraction. The structural motif [Ba2(μ-H)2]2+ was compared with that published in the literature. Hydrogenolysis of the dibenzyl [(Me4TACD)Ca(CH2Ph)2] under the same conditions resulted in decomposition.