The new ethene amidolate motif [OC 1 (H 1 )=C 2 (H 2 )NAr] 2-fills a gap between ethenediolate [OC(H)=C(H)O] 2-and ethenediamidolate [ArNC(H)=C(H)NAr] 2-ligands (Figure ). NBO calculations were undertaken on 32 and 3-THF2 to probe the electronic structure of this species and nature of its binding to magnesium (Figure ). For comparison, the parent [OC 1 (H 1 )=C 2 (H 2 )NAr] 2-was calculated as a non-coordinated dianion. The ethene amidolate adopts a conjugated structure. For 32 the Wiberg Bond Indices (WBIs) take values of C 1 =C 2 (1.57, 1.62), C 1 -O (0.94, 0.94) and C 2 -N (1.25, 1.30). While in the broadest sense, these data can be interpreted in terms of an alternating array of single and double bonds for the ethene amidolate structure, the C-N WBIs are slightly greater than expected for a single bond suggesting a degree of delocalisation of the N lone-pair into the conjugated system. Binding to magnesium is primarily ionic with NPA charges on Mg (+1.82,+1.83) being highly positive and those on O (-1.19,-1.20) and N (-0.91,-0.94) uniformly negative. There also appears to be some differences in the degree of this delocalisation across the different amidoenolates in the calculated structures 32 and 3-THF2 suggesting the ligand can respond and augment its polarisation dependent on the local environment. The molecular orbitals of [OC 1 (H 1 )=C 2 (H 2 )NAr] 2-are consistent with its potential to act as both a -and donor ligand, with the HOMO, HOMO-1 and HOMO-2 showing character of both oxygen and nitrogenbased lone-pairs in the plane and orthogonal to the site of metal coordination (see supporting information). Mechanism: Further calculations were undertaken to shed light on the mechanism that leads to the formation of 32. For simplicity, these calculations were initiated from 2a as the reactant. We have previously calculated insertion of CO into two of the Mg-H bonds of 1a and proposed structures similar to 2a in the homologation and deoxygenation of CO using this tetrametallic cluster. A plausible pathway for ethene amidolate formation was found (Figure ). This pathway parallels the most common pathway described for ethenediolate formation in reactions of metal hydrides with CO. to the cis-isomer of the ethene amidolate ligand, Int-5. The sequence of hydromagnesiation, CO insertion, and 1,2-hydride migration then repeats ultimately leading to the experimentally determined product 32. Analysis of the complete pathway for formation of 32 reveals that the formation of the 1 st and 2 nd ethene amidolate ligands occurs with similar barriers, consistent with the lack of observable intermediates in the conversion of 2a to 32. The global barrier is associated with the 1 st hydride transfer step from 2a and is G ‡ 298K = 28.3 kcal mol -1 which is in reasonable agreement with the experimental conditions for the reaction (14 h, 60 °C).