Carbodicarbene-Stibenium Ion-Mediated Functionalization of C(sp³)-H and C(sp)-H Bonds

Main-group element-mediated C-H activation remains experimentally challenging and the development of clear concepts and design principles has been limited by the increased reactivity of relevant complexes, especially for the heavier elements. Herein, we report that the stibenium ion [(^pyCDC)Sb][NTf₂]₃ (1) (^pyCDC=bis-pyridyl carbodicarbene; NTf₂=bis(trifluoromethanesulfonyl)imide) reacts with acetonitrile in the presence of the base 2,6-di-tert-butylpyridine to enable C(sp³)-H bond breaking to generate the stiba-methylene nitrile complex [(^pyCDC)Sb(CH₂CN)][NTf₂]₂ (2). Kinetic analyses were performed to elucidate the rate dependence for all the substrates involved in the reaction. Computational studies suggest that C-H activation proceeds via a mechanism in which acetonitrile first coordinates to the Sb center through the nitrogen atom in a κ¹ fashion, thereby weakening the C-H bond which can then be deprotonated by base in solution. Further, we show that 1 reacts with terminal alkynes in the presence of 2,6-di-tert-butylpyridine to enable C(sp)-H bond breaking to form stiba-alkynyl adducts of the type [(^pyCDC)Sb(CCR)][NTf₂]₂ (3 a-f). Compound 1 shows excellent specificity for the activation of the terminal C(sp)-H bond even across alkynes with diverse functionality. The resulting stiba-methylene nitrile and stiba-alkynyl adducts react with elemental iodine (I₂) to produce iodoacetonitrile and iodoalkynes, while regenerating an Sb trication.