![]() The importance of polyhapto arene-to-cation binding, for example, during the membrane transport of K + and the structures and function of many enzymes, has prompted intense interest in the nature and specificity of such interactions 23. Non-covalent interactions between alkali metal cations and aromatic π systems are known to play a pivotal role in the regulation of many biological phenomena 21, 22. While the resistance to reduction of the diamidoberyllate unit of 6 may be plausibly ascribed to the presence of its chloride substituent, rationalisation of the group 1-redox reactivity requires a more nuanced consideration of both the heterogeneous molecular (solution) M + and bulk metallic reaction partners. The M’/M + → M’ +/M interconversion and the maintenance of the Be(II) oxidation level during the synthesis of compounds 7– 10, however, suggests that the susceptibility to reduction of both s-block element centres may also be influenced by its local environment. In contrast, reduction potential data associated with the less redox-flexible elements of groups 1 and 2 are generally perceived to be invariant. It is well established that the electrochemical behaviour of transition metal complexes is profoundly affected by changes in coordination number and ligand field strength 20. This interconversion reactivity is summarised in Fig. ![]() 25), while no evidence of reaction was observed when this resultant solution was added to either a sodium mirror or an excess of 5 wt% Na/NaCl. Although a Be–Be bond has very recently been realised in CpBeBeCp 17, our attempt to access a beryllium analogue of compound 3, by either Li or Na reduction of the 2-coordinate beryllium dianilide, 2 ( 8) (Supplementary Fig. Prompted by the now extensive chemistry arising from Mg–Mg bonded β-diketiminates 13, 14, we 15, and others 16, have also sporadically attempted to synthesise analogous Be(I) derivatives. Notably, these processes are triggered by addition of an external Lewis base specific to the group 1 centre that is to maintain its cationic configuration viz, preferential Li + binding by trisamine (Me 6Tren) biases the system toward reduction to potassium, whereas addition of 2,2,2-cryptand induces the deposition of a more lithium-enriched Li/K alloy (Fig. In a startling recent advance, Lu and co-workers have shown that the room temperature stable electride, K +e − ( 1) 8, may be directed toward partially selective self-reduction of either the K + or Li + component leaving the other in its cationic form 9. + e −) species to comproportionate and/or self-reduce 4, 5, 6, 7. The seminal observations of Dye and co-workers’ have highlighted the tendency of alkalide ( + M − where L = typically, a crown ether or cryptand and M = Na, K, Rb, Cs) and electride (i.e. Although, from this perspective, the electrowinning of Li does follow thermodynamic expectations, similar considerations are not conventionally applied in molecular systems. In this water-free and primarily ionic system, therefore, the relative decomposition potentials are better estimated from the respective molar Gibbs free energies of formation (Δ G 0 m) of LiCl (−384.4 kJ mol −1) and KCl (−408.5 kJ mol −1). This observation is nicely borne out by the industrial production of high-purity lithium metal where, and in seeming contradiction of the standard E 0 values, the Li + component is selectively electro-reduced from a molten LiCl–KCl eutectic 3. The commonly cited group 1 potentials are determined under standard/aqueous conditions and, thus, heavily biased by the M + hydration enthalpies (Δ H Hyd), which decline significantly as group 1 is descended (Li + 506 Na + 406 K + 330 Rb + 310 Cs + 276 kJ mol −1). Comparison of E 0 values, however, must always take account of the electrochemical experimental conditions 2. Judged against this criterion alone, the chemical reduction of Li + to lithium metal is thermodynamically non-viable, even by any of its highly electropositive group 1 congeners. ![]() A case in point is provided by the resistance to reduction of the group 1 monocation, M + (M = Li, Na, K, Rb, Cs), the endothermicity of which is reflected by their highly negative potentials 1. An element’s standard reduction potential ( E 0, V) is a regularly applied figure of merit to evaluate its thermodynamic amenability to electron transfer.
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