Activation of Pyrazines by a Mg–Mg-bonded Compound: Reduction, Homocoupling, and Formation of Metallomacrocycles

The α-diimine-ligated Mg–Mg-bonded compound [K(THF)3]2[LMg–MgL] (1, L = [(2,6-iPr2C6H3)NC(CH3)]22–) can effectively promote the reduction of pyrazine (Pyz) and derivatives under ambient conditions. Reaction of 1 with 1 equiv of pyrazines (Pyz, 2-MePyz, and 2,5-Me2Pyz) caused two-electron reduction of pyrazines to the dianion (RnPyz2–), which bridges two [LMg(II)] fragments to yield dinuclear complexes [K(THF)2]2[L2–(THF)MgII(μ-RnPyz2–)MgII(THF)L2–] (2–4). When 2 equiv of pyrazine substrates were used, the tetranuclear square complexes, featuring pyrazine radical anions (2,3-Me2Pyz)•– (5) or reductive C–C coupling of Pyz (6), were isolated. Moreover, in the dinuclear complex [L•–MgII(μ-Phz2–)MgIIL•–] (8), the original dianion of α-diimine, L2–, was oxidized to a monoanion (L•–), and phenazine (Phz) was reduced to a dianion.