The coupling reaction of terminal alkynes with several isonitriles, catalyzed by the neutral organoactinide complexes Cp2*AnMe 2 (Cp* = C5Me5, An = Th, U) or the cationic complex [(Et2N)3U][BPh4], yielded substituted α,β-acetylenic aldimines, in good to excellent yields. The reaction proceeded via a 1,1-insertion of the isonitrile carbon into a metal-acetylide bond, followed by a protonolysis by the acidic proton of the terminal alkyne. Additional insertion products were obtained by altering the catalyst and the reactant ratios. A plausible mechanism for the catalytic reaction is also presented, based on kinetics measurements and thermodynamic studies of the coupling reaction with Cp2*ThMe2 or [(Et2N)3U][BPh4] as catalysts. The reaction is first-order in catalyst and isonitrile and zero-order in alkyne.