Herein is highlighted an original disproportionation mechanism for the formation of hexagonal closed packed cobalt nanoparticles starting from low-valent cobalt complexes. By coupling experimental and theoretical studies, we demonstrate that oleylamine promotes the disproportionation of the starting metal complexes and controls the growth of the nanocrystals, in contrast to the role of reducing reagents proposed elsewhere. We also decipher the sensitivity of the synthesis in regard to the nature of the phosphine and of the halogen ligands in the starting cobalt precursors. Understanding of the mechanism allows the development of a less expensive and less toxic synthesis of these nanoparticles by decreasing the amount of oleylamine in alkane solvents. Finally, an extension of this process is presented and allows reaching size-and shape-controlled nanosphere and nanorod nickel nanoparticles.

An inner-sphere disproportionation mechanism of the Co(I) precursor CoCl(PPh 3 ) 3 is described through a Density Functional Theory study. The essential role of oleylamine in this process is unravelled. A detailed analysis of the electronic structure of Cobalt dimers of the general formula Co 2 Cl 2 L n (L = NH 3 and PH 3 ) demonstrates that electron transfer is triggered by asymetric coordination of amine and phosphine to stabilize a mixed-valence Co(II)À Co(0) dimer. This is consistent with the HSAB statement that both amine and phosphine ligands are required to stabilize the reaction products, respectively Co(II) and Co(0) centers. We propose a quasi-athermic multi-step disproportionation mechanism with low activation barriers where the electron transfer goes through simple ligand exchanges between Co.

The configurational instability of allenyl copper reagents is unveiled. An experimental study highlights the crucial role of Li + and of the reaction temperature in the control of the configurational stability of allenyl copper reagents. A judicious choice of the reaction conditions allows efficient dynamic kinetic resolution processes and gives a one-pot access to homopropargylic alcohols or amines bearing up to four contiguous defined stereogenic centers.