Transformation Of Formazanate At Nickel(Ii) Centers To Give A Singly Reduced Nickel Complex With Azoiminate Radical Ligands And Its Reactivity Toward Dioxygen

The heteroleptic (formazanato)nickel bromide complex LNi(mu-Br)(2)NiL [LH = Mes-NH-N=C(p-tol)-N=N-Mes] has been prepared by deprotonation of LH with NaH followed by reaction with NiBr2(dme). Treatment of this complex with KC8 led to transformation of the formazanate into azoiminate ligands via N-N bond cleavage and the simultaneous release of aniline. At the same time, the potentially resulting intermediate complex L'Ni-2 [L' = HN=C(p-tol)-N=N-Mes] was reduced by one additional electron, which is delocalized across the pi system and the metal center. The resulting reduced complex [L'Ni-2]K(18-c-6) has a S = 1/2 ground state and a square-planar structure. It reacts with dioxygen via one-electron oxidation to give the complex L'Ni-2, and the formation of superoxide was detected spectroscopically. If oxidizable substrates are present during this process, these are oxygenated/oxidized. Triphenylphosphine is converted to phosphine oxide, and hydrogen atoms are abstracted from TEMPO-H and phenols. In the case of cyclohexene, autoxidations are triggered, leading to the typical radical-chain-derived products of cyclohexene.