To circumvent the observed complications, we turned our attention to desymmetrizing the t-BuTACN ligand, with the aim of generating an L3L'X2 framework, which on introduction of the Ca 2+ centre would yield a neutral (TACN)Ca complex without an acidic OH bond. Examination of the precedent for modulation of C3symmetric phenolic TACN ligands, reveals a scarcity of methods for selective mono-functionalization, presumably due to the selectivity issues associated with stochastic approaches. Noteworthily, synthetic routes have been developed from mono-N-alkylated TACN derivatives yielding pentadentate N,N,N,O,O donor ligands. We envisaged a conceptually simple alternative approach in which [K( 6 -benzene)][(t-BuTACN)Ca] (2) is Oalkylated in situ by functionalization of one phenoxide arms (Scheme 2). We opted for a methylation strategy given its limited steric requirements and prevalence in organic synthesis. Accordingly, the reaction of 2 with excess iodomethane affords the neutral complex (t-BuTACN-Me)Ca (4) in excellent yield (see Figure in SI for more details of other functionalization attempts). NMR spectroscopy supports the formation of the target complex, with the two aromatic signals of C3-symmetric 2 being split into six resonances, consistent with desymmetrization of the ligand scaffold in 4. Single crystal X-ray diffraction confirmed the solid-state structure, with the single methylated O-donor giving rise to the longest Ca-O bond of the series of complexes 2-4 (2.407(4) Å, cf. 2.189(4) and 2.214(5) Å for the anionic phenoxide donors).