RESUMO
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.
RESUMO
An inner-sphere disproportionation mechanism of the Co(I) precursor CoCl(PPh3 )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 Co2 Cl2 Ln (L=NH3 and PH3 ) demonstrates that electron transfer is triggered by asymetric coordination of amine and phosphine to stabilize a mixed-valence Co(II)-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.
