Reduction of Na⁺ within a {Mg₂Na₂} Assembly

Abstract

Ionic compounds containing sodium cations are notable for their stability and resistance to redox reactivity unless highly reducing electrical potentials are applied. Here we report that treatment of a low oxidation state {Mg2Na2} species with non-reducible organic bases induces the spontaneous and completely selective extrusion of sodium metal and oxidation of the Mg(I) centers to the more conventional Mg(II) state. Although these processes are also characterized by a structural reorganisation of the initially chelated diamide spectator ligand, computational quantum chemical studies indicate that intramolecular electron transfer is abetted by the frontier molecular orbitals (HOMO/LUMO) of the {Mg2Na2} ensemble, which arise exclusively from the 3s valence atomic orbitals of the constituent sodium and magnesium atoms.

Cooperative dihydrogen activation at a Na(i)2/Mg(i)2ensemble

“…3a). 18 The behaviour of 6 supports an interpretation of its bonding as a tetrametallic ensemble. Most strikingly, treatment with non-reducible bases such as THF (Fig.…”

“…H atoms, apart from H1 and H1 1 , and occluded hexane solvent have been omitted and iso-propyl groups are shown as wireframe for clarity. Selected bond lengths (Å) and angles (1): Mg1-N1 1.9795(13), Mg1-N2 1.9711(14), Na1-C22 2.7776(18), Na1-C33 2.7840(16), Na1-C34 2.7344(16), Na2-N3 2.2895(14), Na2-C1 3.1096(16), Na2-C2 3.0148(17), Na2-C3 2.9391(19), Na2-C4 2.948(2), Na2-C5 3.023(2), Na2-C6 3.1209(18), N1-Mg1-N2 126.44(6), N1-Mg1-N2 126.44(6). Operations to generate symmetry equivalent atoms: 1 À x, 2 À y, 1 À z.…”

“…3b) results in the selective extrusion of metallic sodium and oxidation of the Mg( i ) centres to the more conventional Mg( ii ) state. 18 Although these processes are also characterised by a structural reorganisation of the chelated diamide spectator ligand to form the macrocyclic species 8 , computational studies indicated that intramolecular electron transfer is expedited via the Mg( i )-derived HOMO and Na( i )-derived LUMO. The narrow separation in energy between these frontier orbitals ( ca.…”

“…The sodium atoms are bound in a η 6 -fashion by each of the Dipp substituents of the chelated {SiN Dipp } ligands, but are differentiated by their interactions with an additional diamide dianion that now adopts a {Na2-μ-κ 1 - N ,μ-κ 1 - N ′-Na2′} bridging mode reminiscent of those to Mg in the macrocyclic species 8 . 18 While Na1/Na1 1 engage via further polyhapto interactions with C31–C36 (and C31 1 –C36 1 ) comprising the Dipp substituents of the bridging dianion, the coordination spheres of Na2/Na2 1 are completed by N3/N3 1 . The Mg1–N1 [1.9795(13) Å] and Mg1–N2 [1.9711(14) Å] bonds of 9 are significantly shorter than the Mg–N distances observed in 6 (avg.…”

Reduction of K+ or Li+ in the Heterobimetallic Electride K+[LiN(SiMe3)2]e–

“…A primary obstacle is the lack of an appropriate reductant to overcome the formidably negative redox potential. Very recently, the Harder group (in 2021 14 ) and the Hill/McMullin groups (in 2023 15 ) reported reducing Na + to zero-valent Na metal, facilitated by favorable inner-sphere electron transfer from electron-rich magnesium(0) 14 or magnesium(I) 15 species, respectively. These two remarkable breakthroughs still have two limits to overcome: (1) The systems require specially designed ligands to bring together the Na + and Mg(0)/Mg(I) fragments to facilitate the electron transfer.…”