The widely used preparation of Ni-0 nanoparticles from [Ni(acac)(2)] (acac=acetylacetonate) and oleylamine, often considered to be a thermolysis or a radical reaction, was analyzed anew by using a combination of DFT modeling and designed mechanistic experiments. Firstly, the reaction was followed up by using TGA to evaluate the energy barrier of the limiting step. Secondly, all the byproducts were identified using NMR spectroscopy, mass spectrometry, FTIR, and X-ray crystallography. These methods allowed us to depict both main and side-reaction pathways. Lastly, DFT modeling was utilized to assess the validity of this new scheme by identifying the limiting steps and evaluating the corresponding energy barriers. The oleylamine was shown to reduce the [Ni(acac)(2)] complex not through a one-electron radical mechanism, as often stated, but as an hydride donor through a two-electron chemical reduction route. This finding has strong consequences not only for the design of further nanoparticles syntheses that use long-chain amine as a reactant, but also for advanced understanding of catalytic reactions for which these nanoparticles can be employed. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.