Abstract
AbstractAn improved synthetic procedure is reported for the hybrid ligand HL, composed of two TACN macrocycles bridged by a central pyrazole moiety. Detailed NMR spectroscopic characterization showed that asymmetry in this dinucleating organic scaffold can be induced at room temperature through the use of anhydrous conditions, owing to pyrazole‐NH prototropy. Thermally induced line broadening allowed for an estimation of the thermodynamic parameters for this proton exchange reaction, giving ΔH‡ = 46.7 kJ·mol–1 and ΔS‡ = –74.2 J·mol–1·K–1. Crystallization of a key intermediate is a crucial aspect of the synthetic improvement, characterization of which revealed an intramolecular hydrogen bond between a sidearm heteroatom and the pyrazole‐NH proton. Protonation of the macrocyclic sidearms in [H3L](BF4)2 allowed for exploration of the influence that this interaction has on the tautomerism, which may in turn potentially be exploited to produce heterobimetallic systems. Structural characterization of the corresponding sodium salt NaL gave further insights into the general coordination behavior of HL.
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