Mechanistic insight into the N=N bond-cleavage of azo-compounds that was induced by an Al-Al-bonded compound [L(2-)Al(II)-Al(II)L(2-)

An α-diimine-stabilized Al-Al-bonded compound L(2-)Al(II)-Al(II)L(2-)] (L = {(2,6-iPr(2)C(6)H(3))NC(Me)}(2)]; 1) consists of dianionic α-diimine ligands and sub-valent Al(2+) ions and thus could potentially behave as a multielectron reductant. The reactions of compound 1 with azo-compounds afforded phenylimido-bridged products L(-)Al(III)(μ(2)-NPh)(μ(2)-NAr)Al(III)L(-)] (2-4). During the reaction, the dianionic ligands and Al(2+) ions were oxidized into monoanions and Al(3+), respectively, whilst the NAr](2-) imides were produced by the four-electron reductive cleavage of the N=N double bond. Upon further reduction by Na, the monoanionic ligands in compound 2 were reduced to the dianion to give (L(2-))(2)Al(III)(2)(μ(2)-NPh)(2)Na(2)(thf)(4)] (5). Interestingly, when asymmetric azo-compounds were used, the asymmetric adducts were isolated as the only products (compounds 3 and 4). DFT calculations indicated that the reaction was quite feasible in the singlet electronic state, but the final product with the triplet-state monoanionic ligands could result from an exothermic singlet-to-triplet conversion during the reaction process.