Combined, these observations show that upon deprotonation of the secondary amine, the methylene linker on the same side becomes more acidic and gets subsequently deprotonated by the second equiv of KOt-Bu. This unexpected deprotonation of the dipp DAMN ligand led us to set our sights on a ligand design without methylene protons. By substituting the pendant secondary amines with pendant amides, we expected to retain the binding features dipp DAMN whilst supressing the observed deprotonation of the methylene linkers. Additionally, the appearance of the -CH 3 protons as a single (albeit broad) doublet at δ = 1.60 ppm which integrates to 24 H, suggests that the previously proposed constrained rotation of the N-C Ar bonds might be alleviated upon sequestration of K + . Layering a saturated toluene solution of 2•2(18-c-6) with pentane resulted in the formation of single crystals, suitable for X-ray diffraction. Elucidation of the crystal structure (Figure ) revealed the dimeric nature of 2•2(18-c-6) in the solid-state. Two independent crown ether-sequestered K + ions are found per naphthyridine motif, residing above and below the naphthyridine plane, respectively. The dipp NDC ligands are bound to K + via the imidate (via oxygen) binding mode rather than the amidate (via nitrogen) binding mode, with K-O (lig) distances of 2.553(3) Å and 2.744(3) Å. There is a short contact between one of the sequestered potassium cations and a methyl group on one of the dipp groups of the other molecule in the dimer. This short K•••C contact of 3.415(4) Å is within the range of reported examples of -CH 3 to K + agostic bonding where the K + is sequestered by 18-crown-6. We hypothesised that transmetalation of 2•2(18-c-6) with metal precursors would most likely result in the retention of the imidate binding mode (see below). To investigate if we could access the amidate form of the ligand, we attempted direct metalation of the N-H bond using Grignard reagents, which contain an internal base. A reaction between dipp NDC and two equiv MeMgCl resulted in a bright orange solution concomitant with visible effervescence. From this mixture, 3 was isolated as a yellow solid in 74% yield (Scheme 5, left). Analysis of the 1 Hand in line with full deprotonation of the dipp NDC ligand. Layering a saturated solution of 3 in THF with hexane and storing it at -40 °C for several days yielded orange single crystals suitable for analysis by X-ray diffraction. The solid-state structure of 3 ( dipp NDCMg 2 Cl 2 •4THF, Figure ) revealed the formation of a dinuclear complex containing two independent Mg centres, one in each of the binding pocket of the dipp NDC ligand. Similar to 2•2(18-c-6), the imidate binding mode was obtained in the solid-state structure rather than the amidate binding mode, suggesting that the ligand readily tautomerises upon deprotonation. Two THF molecules (cis to each other) are bound to each Mg centre and together with the bridged chloride ligands a distorted octahedral geometry around Mg is obtained. The two Mg centres are positioned slightly outside of the naphthyridine plane (see ESI Figure ), with the orientation of the axial ligands per centre being antiparallel. The combination of this geometry with the variety of ligands on the Mg centres results in optical isomerism, with both the Λ,Λ and Δ,Δ compounds being formed in solution. The analysed crystal was comprised of a single enantiomer of 3 (Δ,Δ). Having obtained structural insights and spectroscopic handles of 3, we reacted 2•2(18-c-6) with 2 equiv of MgCl 2 in THF. H NMR analysis of the reaction mixture showed 3 as the major product, thereby confirming our aforementioned hypothesis that this reaction would yield the imidate tautomer (see ESI Figure ). dipp DAMNMg 2 Cl 2 •2 THF: The imidate binding mode found for 2 and 3 decreases the steric pressure around the dimagnesium core due to steric bulk of the dipp groups pointing away from the dinuclear core. In order to investigate the influence the decrease in steric bulk around the Mg 2 Cl 2 core has on its coordination chemistry, we targeted the synthesis of the Mg 2 Cl 2 complex of the dipp DAMN ligand for direct comparison with 3. Addition of dipp DAMN to a THF solution of 2 equiv of MeMgCl led to clean formation of 4 as a bright orange solid in quantitative yield (Scheme 5, right). Analysis of the 1 H-NMR and C{ 1 H}-NMR spectra (C 6 D 6 , 298 K) showed a number of resonances consistent with retention of the C 2v -symmetry of the ligand (see ESI Section 1.9). The loss of the N-H resonances, the presence of only two naphthyridine resonances (δ = 7.00 and 6.61 ppm) and the appearance of a singlet at δ = 5.08 ppm integrating to 4H, which we attribute to the methylene linkers, all suggested that the secondary amines are selectively deprotonated by the methyl groups of the Grignard reagent, contrasting the deprotonation order observed for 1. In addition, broad resonances are observed at δ = 3.65 and 1.25 ppm suggesting that THF is bound to the Mg centres in solution. Layering a saturated THF solution of 4 with pentane at -40°C led to the formation of orange needles suitable for analysis by X-ray diffraction. The solid-state structure of 4 (Figure ) agrees with the spectroscopic data and confirms the selective deprotonation of the N-H protons by the Grignard reagent, with each Mg centre residing in a bidentate binding pocket of the dinucleating ligand. In the crystal, 4 is located on a mirror plane. The two chlorides bridge the two Mg centres in a "diamond core" fashion and a THF ligand per Mg completes the observed trigonal bipyramidal geometry (τ = 0.75), with the naphthyridine N-donor and the THF O-donor occupying the axial positions. The bond between the naphthyridine N-donor and Mg (Mg1-N1 = 2.234(3) Å) is substantially longer than the bond between Mg and the pendant amine (Mg1-N2 = 1.979(3) Å), consistent with the neutral and anionic character of these donors, respectively. 34