A Brønsted Acidic Gallium Hydride: Facile Interconversion of NNNN-Macrocycle Supported [GaI ]+ and [GaIII H]2
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Updated: Oct 9, 2025

Characterizing Lewis Pairs Using Titration Coupled with In Situ Infrared Spectroscopy
Published on: February 20, 2020
Louis J Morris1, Priyabrata Ghana1, Thayalan Rajeshkumar2
1Institute for Inorganic Chemistry, RWTH Aachen University, 52062, Aachen, Germany.
Abstract:
Protonolysis of [Cp*M] (M=Ga, In, Tl) with [(Me4 TACD)H][BAr4 Me ] (Me4 TACD=N,N',N'',N'''-tetramethyl-1,4,7,10-tetraazacyclododecane; [BAr4 Me ]- =[B{C6 H3 -3,5-(CH3 )2 }4 ]- ) provided monovalent salts [(Me4 TACD)M][BAr4 Me ], whereas [Cp*Al]4 yielded trivalent [(Me4 TACD)AlH][BAr4 Me ]2 . Protonation of [(Me4 TACD)Ga][BAr4 Me ] with [Et3 NH][BAr4 Me ] gave an unusually acidic (pKa (CH3 CN)=24.5) gallium(III) hydride dication [(Me4 TACD)GaH][BAr4 Me ]2 . Deprotonation with IMe4 (1,3,4,5-tetramethyl-imidazol-ylidene) returned [(Me4 TACD)Ga][BAr4 Me ]. These reversible processes occur with formal two-electron oxidation and reduction of gallium. DFT calculations suggest that gallium(I) protonation is facilitated by strong coordination of the tetradentate ligand, which raises the HOMO energy. High nuclear charge of [(Me4 TACD)GaH]2+ facilitates hydride-to-metal charge transfer during deprotonation. Attempts to prepare a gallium(III) dihydride cation resulted in spontaneous dehydrogenation to [(Me4 TACD)Ga]+ .
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