Head-to-Head Homocoupling of Ynamides via a Dual Activation Mode of Triple Bonds by Half-Sandwich Metal Complexes

Reported herein is the half-sandwich Rh-mediated head-to-head homocoupling of terminal ynamides to furnish dienyl bisamido rhodacyclic complexes, where the Rh–vinyl bond was formed selectively at the α-carbon to the nitrogen atom. This transformation was extended to include piano-stool Ru and Ir complexes to display an analogous homocoupling reactivity. Based on density functional theory studies, the reaction was proposed to proceed via a dual activation mode of the ynamide triple bonds: (i) generation of a zwitterionic keteniminyl metal species to induce an intramolecular chloride transfer and (ii) syn-carbometallation of the second coordinated alkynes by the alkenyl metal intermediate. An oxidative transformation of the homocoupled metal complexes gave multifunctional dienyl bisamide compounds.