Facile Access to Organostibines via Selective Organic Superbase Catalyzed Antimony-Carbon Protonolysis

The selective formation of antimony-carbon bonds via organic superbase catalysis under metal- and salt-free conditions is reported. This novel approach utilizes electron-deficient stibine, Sb(C₆F₅)₃, to give upon base-catalyzed reactions with weakly acidic aromatic and heteroaromatic hydrocarbons access to a range of new aromatic and heteroaromatic stibines, respectively, with loss of C₆HF₅. Also, the significantly less electron-deficient stibines, Ph₂SbC₆F₅ and PhSb(C₆F₅)₂ smoothly underwent base-catalyzed exchange reactions with a range of terminal alkynes to generate the stibines of formulae PhSb(C≡CPh)₂, and Ph₂SbC≡CR [R=C₆H₅, C₆H₄-NO₂, COOEt, CH₂Cl, CH₂NEt₂, CH₂OSiMe₃, Sb(C₆H₅)₂], respectively. These formal substitution reactions proceed with high selectivity as only the C₆F₅ groups serve as a leaving group to be liberated as C₆HF₅ upon formal proton transfer from the alkyne. Kinetic studies of the base-catalyzed reaction of Ph₂SbC₆F₅ with phenyl acetylene to form Ph₂SbC≡CPh and C₆HF₅ suggested the empirical rate law to exhibit a first-order dependence with respect to the base catalyst, alkyne and stibine. DFT calculations support a pathway proceeding via a concerted σ-bond metathesis transition state, where the base catalyst activates the Sb-C₆F₅ bond sequence through secondary bond interactions.