Acidity Quantification and Structure Analysis of Amide-AlCl₃ Liquid Coordination Complexes for C₄ Alkylation...

Liquid coordination complexes (LCCs), which are formed between metal halides and donor molecules, represent promising catalysts. Six amide-AlCl₃ LCCs were successfully synthesized, followed by their characterization through NMR, Raman, and UV-visible spectroscopy. The acidity of these LCCs was quantified by performing computational modelling of fluoride ion affinities (FIA) and experimental Gutmann-Beckett measurements. Spectroscopic analysis indicated bidentate coordination between amide ligands and Al, which induced asymmetric splitting of Al₂Cl₆ into diverse ions such as [AlCl₂L₂]⁺, [AlCl₄]^-, [AlCl₃L], and [Al₂Cl₆L]. The computed FIA was found to align well with the experimental acidity trends, thereby confirming the proposed structure of the LCC. In the alkylation tests, the LCC with a high acidity demonstrated an increase in the yields of C₅-C₇ alkylates. These results provide an in-depth understanding of the tuneable structures of amide-AlCl₃ LCCs. The acidity of LCCs can be controlled by tuning the ratio of the organic ligand to AlCl₃, which allows bidentate coordination to facilitate asymmetric splitting of Al₂Cl₆. The LCCs demonstrate a high degree of potential as versatile and sustainable acid catalysts in alkylation reactions. These findings may advance the foundational knowledge of LCCs for the purpose of targeted acid catalyst design.