Triazolato Pd(II) and Pt(II) complexes of 2,6-bis(1-ethylbenzimidazol-2′-yl)pyridine formed via catalyst-free [3 + 2] click reactions

At the ambient temperature and under catalyst-free conditions, reactions between [MN₃(L^ET)]PF₆ (M = Pd(II) and Pt(II); L^ET = 2,6-bis(1-ethylbenzimidazol-2′-yl)pyridine) and substituted alkynes (dimethyl acetylene-dicarboxylate and 4,4,4-trifluoro-2‑butynoic acid ethyl ester) afforded the corresponding triazolate complexes. These reactions produced a mixture of triazolate bound isomers. The N1 triazolate isomer of the Pt(II) complexes, which first appeared in the [3 + 2] coupling, eventually isomerized to the N2-analogue during the incubation in DMSO. The reactions of [MN₃(L^ET)]PF₆ with asymmetric alkyne, 4,4,4-trifluoro-2‑butynoic acid ethyl ester, produced a mixture of the three anticipated triazolate isomers, according to ¹⁹F NMR spectroscopy. The stability of the triazolate complexes was investigated, along with the cycloaddition reaction's mechanism and the nature of the intermediates, using NMR spectroscopy.