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

Two complementary catalytic systems are reported for the 1,3-dipolar
cycloaddition of azides and iodoalkynes. 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) metallacycle or via direct π-activation
of the starting iodoalkyne.