To gain insight into the electronic structure of the NHGe motif in 2 and 3, and the extent of Ge-Zn interactions in the latter, Density Functional Theory (DFT) and Natural Bond Orbitals (NBO) calculations were performed. The bond metrics of the geometry-optimised structure in the gas phase of 2 are in agreement with our proposed two-electron reduction of the naphthyridine pocket that coordinates the Ge(II) centre (for more details, see ESI Section 2.5 and Table ). In the gas-phase optimised geometry of 3 (see ESI Section 2.7), the calculated Ge-Zn distance is significantly shorter than the experimental distance (2.861 Å vs. 3.1110(8) Å). This difference in the Ge-Zn distance remains even when the calculations are performed without any empirical dispersion (2.868 Å, see ESI Section 2.8). Because distance can be an important factor when investigating the extent of electronic interactions, we ran calculations on both the freely optimised gas-phase structure of 3 (a) and a structure where the Ge-Zn distance was fixed at the distance obtained from the solid-state structure (b, see ESI Section 2.9). It is worth mentioning that both 3a and 3b underestimate one of the Ge•••Cl distances by approx. 0.5 Å. Analysis of the frontier Kohn Sham orbitals of 2 revealed a delocalised bonding interaction spanning the N-Ge-N motif of the NHGe in the HOMO, along with antibonding interactions between Ge and the two N-donors in the LUMO and LUMO+1 orbitals (see ESI Figure ). Using NBO analysis, we further explored the electronic structure of 2, 3a, and 3b. The partial dearomatisation of the naphthyridine backbone and the presence of a C=C bond located outside of the naphthyridine ring system (on the Ge side) were both observed in the Lewis structure on which the NBO calculations of 2, 3a, and 3b converged. According to the calculations, the π-bonding interaction along the N-Ge-N motif is best described as a 3-centre-4-electron (3c4e) hyperbond (see ESI Figure ), which is in agreement with the reported electronic structure of related 5-membered N-heterocyclic tetrylenes. Structurally this can best be visualised as the superposition of the neutral germylene resonance structure (B) and the two ylide structures (A, C) depicted in Scheme 4. For 5membered NHGe motifs like the one found in 2 and 3, an additional resonance structure has been proposed based on spectroscopic and reactivity studies: the so-called 'chelated atom' structure (Scheme 4, D). Based on the calculated bond metrics of the NHGe motif in both complexes, the contribution of this resonance structure -a formally Ge(0) centre stabilised by a diazabutadiene fragment -appears minor. Nonetheless, we envision that germylone-like reactivity of 2 and 3 is possible, based on the reported four-electron reactivity of a structurally similar iminopyridinegermylene complex, where the Ge centre is oxidised to Ge(IV) while also acting as conduit for the electrons stored in the redox-active ligand. Germanium being one of the heavier tetrels, the germylene lone pair of 2 resides in an orbital of mostly s-character (87%, 13% p-character, ESI Figure ), due to poor mixing of the s-and p-orbitals and hence lack of hybridisation. Similarly, the Ge lone pair of 3a and 3b resides in a spherically diffuse orbital of mostly s-character (90%). Second-order perturbation analysis revealed a delocalisation energy of 15.2 kcal•mol -1 from the Ge lone pair donor NBO of 3a to a Zn-based acceptor NBO of s-character (>99%). The same interaction for 3b (Figure ) has a delocalisation energy of 6.7 kcal•mol -1 , consistent with the larger Ge-Zn separation and the resulting decrease in overlap between the donor and acceptor NBOs. Both interactions are small compared to the calculated interactions found between Zn and the N-donors (32-40 kcal•mol -1 ) and Zn and the Cl-donors (68-90 kcal•mol -1 ). Additionally, the calculations do not reveal any additional interactions from Zn to Ge. We subsequently investigated if the remaining binding pocket could be reduced. Treatment of a THF solution of 2 with a slight excess (2.5 equiv) of fine mesh (325) Mg 0 powder results in the formation of a dark green solution of 4, a highly reactive compound that decomposes upon complete removal of the solvent (Scheme 5). 1 H-NMR analysis of 4 in THF-d 8 (see ESI Section 1.6) revealed four equally integrating naphthyridine resonances in the range of δ = 6.27-5.04 ppm. In contrast to the spectroscopic data of 2, no methine resonance with aldimine character was observed, with the two singlets attributed to the methine resonances being found at an upfield chemical shift of δ = 6.50 and 5.37 ppm. Combined, these observations are consistent with the two-electron reduction of the previously empty pocket (and formal four-electron reduction of the ligand), likely with a Mg centre being bound in a similar fashion as to a monomer of 1. The observed decomposition upon complete removal of the solvent implies that THF molecules are bound to 4. Combined with our NMRspectroscopic observations, we propose a structure for 4 as depicted in Scheme 5. Whilst the cooperative reactivity of germylene-transition metal complexes is well-documented, analogous transformations involving main-group partners have remained elusive. We therefore turned our attention to investigating whether 4 could enable (cooperative) bond activation. The addition of p-tolylacetylene to a THF solution of 4 resulted in the formation of a green solution within 5 minutes (Scheme 6, top-left). The four doublets attributed to the naphthyridine protons are found relatively upfield (δ = 5.54-4.71 ppm) and the chemical shift of the two singlets attributed to the sidearm protons (δ = 5.57 and 5.07 ppm) is more consistent with assignment to an enamide character of these protons over an aldimine character. The presence of two coupling doublets at δ = 7.27 and 6.97 ppm ( 3 J H,H = 8.1 Hz, 2H each) and a singlet at δ = 2.23 ppm (3H), are indicative of one equivalent of p-tolylacetylene being bound. We attribute the singlet at δ = 7.38 (1H) ppm to the terminal proton of the former acetylene fragment. Through a combination of 2D NMR experiments we were able to confirm the addition of one of the unsaturated C-C bonds of p-tolylacetylene over the Ge centre and the methine, resulting in a bicyclo[2,2,1]heptane motif (Scheme 6).