A monomeric nickel-dioxygen adduct derived from a nickel(I) complex, and O2

The nickel(I) complex [PhTt(Ad)]Ni(CO) (PhTt(Ad), phenyltris((1-adamantylthio)methyl)borate) reacts with O-2 generating a 1:1 species identified as a side-on dioxygen adduct based on its spectroscopic properties as supported by DFT computational results and by its reactivity. The Ni EXAFS data are fit to a S3O2 coordination environment with short Ni-O distances, 1.85 Angstrom. The brown complex displays a rhombic EPR signal with g values of 2.24, 2.19, 2.01. DFT and INDO/S-Cl computations replicate the EXAFS and EPR features and suggest that 2 is a side-on [NiO2](+) complex with geometric and electronic properties that are best rationalized in terms of a highly covalent Ni(II)-superoxo description. [PhTt(Ad)]-Ni(O-2) oxidizes PPh3 to OPPh3, NO to NO3-, and [PhTt(tBu)]Ni(CO) to the nonsymmetric [PhTt(Ad)]Ni(mu-O)(2)Ni[PhTt(tBu)] dimer.