Mechanistic study of gold(l)-catalyzed lntermolecular hydroamination of alienes

The intermolecular hydroamination of alienes occurs readily with hydrazlde nucleophlles, In the presence of 3-12% Ph₃PAuNTf₂. Mechanistic studies have been conducted to establish the resting state of the gold catalyst, the kinetic order of the reaction, the effect of ligand electronics on the overall rate, and the reversibility of the last steps in the catalytic cycle. We have found the overall reaction to be first order In gold and aliene and zero order in nucleophile. Our studies suggest that the rate-limiting transition state for the reaction does not involve the nucleophile and that the active catalyst Is monomeric in gold(l). Computational studies support an "outersphere" mechanism and predict that a two-step, no intermediate mechanism may be operative. In accord with this mechanistic proposal, the reaction can be accelerated with the use of more electron-deficient phosphine ligands on the gold(l) catalyst.