Fluorinated Anions Promoted “on Water” Activity of Di- and Tetranuclear Copper(I) Catalysts for Functional Triazole Synthesis

A set
of di- and tetra-copper­(I) compounds [Cu2(L1H)2]­[BArF]2 (1) (L1H = bis­(5,7-dimethyl-1,8-naphthyridin-2-yl)­amine;
BArF = [B­{C6H3(CF3)2}4]) and [Cu4(L1)2(L2)2]­[BNBF]2 (2) (L2 = 5,7-dimethyl-1,8-naphthyridin-2-amine;
BNBF = [NH2{B­(C6F5)3}2]), stabilized by naphthyridine-based ligands
and containing fluorinated anions, is synthesized. Their catalytic
utility for copper­(I)-catalyzed azide–alkyne coupling (CuAAC)
reactions in organic solvents and “on water” is evaluated.
The dimer analogue [Cu2(L1H)2]­[BPh4]2 (3) with nonfluorinated anion is
synthesized for the purpose of comparison. All three compounds show
CuAAC activity in organic solvents, although the performance of 3 is considerably lower. Remarkable rate enhancement is displayed
by compounds containing fluorinated anions (1 and 2) under “on water” conditions for the model
reaction involving benzyl azide, affording 98% conversions in 15–20
min, where compound 3 gives 76% conversions in 50 min.
Kinetic experiments reveal the involvement of two coppers in the cycloaddition
process. Employing a host of substrates, the usefulness of fluorinated
anions to dramatically improve the catalytic activity of Cu­(I) compounds
under “on water” conditions is demonstrated.