Catalytic and Computational Studies of N-Heterocyclic Carbene or Phosphine-Containing Copper(I) Complexes for the Synthesis of 5-lodo-1,2,3-Triazoles

Two complementary catalytic systems are reported for the 1,3-dipolar cydoaddition of azides and iodoallcynes. These are based on two commercially available/readily available copper complexes, [CuCl(IPr)] or [CuI(PPh3)(3)], which are active at low metal loadings (PPh3 system) or in the absence of any other additive (IPr system). These systems were used for the first reported mechanistic studies on this particular reaction. An experimental/computational-DFT approach allowed to establish that (1) some iodoalkynes might be prone to dehalogenation under copper catalysis conditions and, more importantly, (2) two distinct mechanistic pathways are likely to be competitive with these catalysts, either through a copper(III) metallacyde or via direct pi-activation of the starting iodoalkyne.