A Brønsted Acidic Gallium Hydride: Facile Interconversion of NNNN‐Macrocycle Supported [GaI]+ and [GaIIIH]2

Protonolysis of [Cp*M] (M=Ga, In, Tl) with [(Me4TACD)H][BAr4Me] (Me4TACD=N,N′,N′′,N′′′‐tetramethyl‐1,4,7,10‐tetraazacyclododecane; [BAr4Me]−=[B{C6H3‐3,5‐(CH3)2}4]−) provided monovalent salts [(Me4TACD)M][BAr4Me], whereas [Cp*Al]4 yielded trivalent [(Me4TACD)AlH][BAr4Me]2. Protonation of [(Me4TACD)Ga...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2022-03, Vol.61 (11), p.e202114629-n/a
Main Authors: Morris, Louis J., Ghana, Priyabrata, Rajeshkumar, Thayalan, Carpentier, Ambre, Maron, Laurent, Okuda, Jun
Format: Article
Language:English
Subjects:
Cations
Charge transfer
Dehydrogenation
Dihydrides
Energy charge
Gallium
Group 13 Elements
Hydrides
Macrocyclic Ligands
Oxidation
Protonation
Redox Chemistry
Salts
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Summary:Protonolysis of [Cp*M] (M=Ga, In, Tl) with [(Me4TACD)H][BAr4Me] (Me4TACD=N,N′,N′′,N′′′‐tetramethyl‐1,4,7,10‐tetraazacyclododecane; [BAr4Me]−=[B{C6H3‐3,5‐(CH3)2}4]−) provided monovalent salts [(Me4TACD)M][BAr4Me], whereas [Cp*Al]4 yielded trivalent [(Me4TACD)AlH][BAr4Me]2. Protonation of [(Me4TACD)Ga][BAr4Me] with [Et3NH][BAr4Me] gave an unusually acidic (pKa(CH3CN)=24.5) gallium(III) hydride dication [(Me4TACD)GaH][BAr4Me]2. Deprotonation with IMe4 (1,3,4,5‐tetramethyl‐imidazol‐ylidene) returned [(Me4TACD)Ga][BAr4Me]. 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 [(Me4TACD)GaH]2+ facilitates hydride‐to‐metal charge transfer during deprotonation. Attempts to prepare a gallium(III) dihydride cation resulted in spontaneous dehydrogenation to [(Me4TACD)Ga]+. Protonation of an NNNN‐macrocycle chelated gallium(I) cation provides a rare dicationic gallium(III) hydride. This process is easily reversed by treatment of the Brønsted acidic (pKa=24.5) hydride with a neutral base. Similar facile redox cycling was not observed for analogous aluminium, indium, or thallium systems.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.202114629