A careful methodological study revealed a true Click catalytic system based on commercially available [CuBr(PPh(3))(3)]. This system is active at room temperature, with 0.5 mol % [Cu] (or less), in the absence of any additive, and it does not require any purification step to isolate pure 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.

The preparation of novel phosphinite- and phosphonite-bearing copper(I) complexes of the general formula [CuX(L)] is reported. These compounds, which remain scarce in the literature, could be prepared using readily available starting materials and were spectroscopically and structurally characterized. These complexes, together with their known phosphine and phosphite analogues, were then applied to the 1,3-dipolar cycloaddition of azides and alkynes, to find that the new complexes displayed the best activities. Full optimization of the reaction conditions resulted in a noteworthy Click catalytic system, active under very mild reaction conditions in the absence of any additive and using low metal loadings.

The remarkable activity displayed by copper(I)–phosphinite complexes of general formula [CuBr(L)] in two challenging cycloadditions is reported: a) the one‐pot azidonation/cycloaddition of boronic acids, NaN3, and terminal alkynes; b) the cycloaddition of azides and iodoalkynes. These air‐stable catalysts led to very good results in both cases and the expected triazoles could be isolated in pure form under ‘Click‐suitable’ conditions.

CuBr(PPh 3 ) 3 ] for Azide-Alkyne Cycloaddition Reactions under Strict Click Conditions. -[CuBr(PPh3)3] allows formation of a wide range of 1,4-disubstituted triazoles under mild conditions. In situ preparation of azides is possible. -(LAL, S.; DIEZ-GONZALEZ*, S.; J. Org. Chem. 76 (2011) 7, 2367-2373, http://dx.