Copper complexes bearing C-scorpionate ligands: Synthesis, characterization and catalytic activity for azide-alkyne cycloaddition in aqueous medium

Reactions of CuX (X = Br or I) and [Cu(MeCN)₄][BF₄] with the neutral C-scorpionates HC(3,5-Me₂pz)₃ and HC(3-Phpz)₃ (Tpm^∗ and Tpm^Ph, respectively) proceed readily at room temperature to give the neutral copper(I) complexes [CuBr(Tpm^Ph)] (1), [CuI(Tpm^Ph)] (2), [CuBr(Tpm^∗)] (3), [CuI(Tpm^∗)] (4) and the cationic [Cu(Tpm^Ph)(NCMe)][BF₄] (5), [Cu(Tpm^∗)(NCMe)][BF₄] (6) and [Cu(Tpm^∗)₂][BF₄]₂ (7), the latter also obtained from 6 after some time in air. Compounds 1–7 act as homogeneous catalysts for the low-power microwave-assisted three component (alkyne, bromobenzyl, sodium azide) cycloaddition reaction (CuAAC) to afford 1,4-disubstituted-1,2,3-triazoles, with 7 as the best catalyst. The catalytic reaction evolves well in ROH/H₂O solution, depends on the R group and proceeds better when R = Me, here achieving yields up to 94%. The alcohol plays a role in the Cu(II)-to-Cu(I) Glaser-type induction period, therefore avoiding a reducing agent in the system.