The energy barrier is only 11.0 KJ/mol. Thus, in MeOH, formate coordinates to the metal preferentially by its hydrogen rather than its oxygen atom, at least as a first step. Subsequently, the complex rearranges, passing through another transition state in which the formate rotates: the energy of (Mn•••H-CO2 -) TS is only 2.9 KJ/mol higher than the As mentioned earlier, adducts generated from diluted amine-CO2 solutions (Figure a-f) should take part in this catalytic scenario, by either activating some reactive species (such as dissolved CO2) and/or by stabilizing key transition states. With the exception of TMEDA, all amines display a similar TONH2. This strongly suggests that the main source of protons in solution is MeOH rather than the ammonium moieties paired with carbamates or carbonates. TMEDA stands as an extreme case in the series, markedly favoring H2 over formate. The conversion of this α,β-diamine into a bisammonium dication upon double carbonation is strongly disfavored, therefore its main adduct with CO2 combines a basic nitrogen moiety and an ammonium group (species 1c-TMEDA, Figure ). This Lewis acid-base pair (or dipole) can activate the reactivity of the MeOH dipolar species toward HMn, thereby leading to an increased H2 production. PMDETA, which formally results from the chain elongation of TMEDA, should act similarly. Yet, dicarbonation does occurs in substantial amount on this species, yielding an α,ωbisammonium bearing a central neutral nitrogen (Figure , 2c-PMDETA and supporting section 7). This quadrupolar species perfectly meets the requirements to activate a complementary quadrupolar species, such as CO2 (Figure and). Preliminary calculations at the AM1 level (Figure , bottom) confirm this electrostatic complementarity and affinity (with the starting material, dissolved CO2, and the product, the formate anion). It also highlights the activating role of PMDETA, as CO2 binding is accompanied by its bending by 5°, which pre-activates this substrate toward hydride addition (figure , bottom). Additional DFT calculations confirm this interpretation. The divalent ammonium-bicarbonate salt 2c-PMDETA does not only bind quite strongly to CO2 (computed ΔG=-9.7 KJ/mol), but the reaction with the reduced Mn hydride radical anion HMn - proceeds barrierless toward the production of formate, which is coordinated to Mn metal via the H atom (see last row in Table ). The catalytic cycle then proceeds as previously described and illustrated in Table . Thus, the limiting step of the whole catalytic cycle is apparently no longer CO2 activation, but the competing coordination of CO2, bicarbonate, formate and water to 2c-PMDETA. Indeed, DFT calculations suggest high formation constants between 2c-PMDETA and bicarbonate (-126.9 KJ/mol) and formate (-129.8 KJ/mol). The model described in this paragraph, based on the ability of absorbents to generate dipolar or quadrupolar CO2 capture adducts in significant amounts, which should respectively activate complementary dipoles or quadrupoles such as methanol or CO2 and enhance the production of H2 or formate, remains valid on the rest of the series. DETA stands in between the two extreme cases of PMDETA and TMEDA and moderately enhances the selectivity toward formate production. We recently reported that DETA-CO2 is a compositionally complex system in methanol which is herein even further complexified by the presence of water (Figure ). While some methanol activating dipolar patterns can be found on some members of the DETA-based library of carbamates and carbonates (such as species 1c-DETA, 1a-DETA and 1s-DETA, Figure ), the presence of appended charges or polar moieties seems to prevent any enhancement of H2 production. The bisammonium biscarbonate homologue of the 2c-PMDETA adduct, noted 2c-DETA is present in this complex system, but its relatively lower concentration and higher hydrophilicity (which decreases the availability of the ammonium moieties for lone pair binding) moderates the enhancing effect toward formate production. The other amines of the series behave as negative controls (Figure , 4e and 4f): triethylammonium only displays a single acidic site while the free doublets on TBG are orthogonal to the lone pair of the only free nitrogen site. DEA bears two alcohol end groups, which may act as moderate H-bond donating sites, but in its loaded form, it misses the central nucleophilic nitrogen, to properly play the co-factor role imputed to 2c-PMDETA quadrupole.