A discrete, dicopper μ-alkynyl complex, [Cu<sub>2</sub>(μ-η<sup>1</sup>:η<sup>1</sup>-C≡C(C<sub>6</sub>H<sub>4</sub>)CH<sub>3</sub>)DPFN]NTf<sub>2</sub> (DPFN = 2,7-bis(fluoro-di(2-pyridyl)methyl)-1,8-naphthyridine; NTf<sub>2</sub><sup>-</sup> = N(SO<sub>2</sub>CF<sub>3</sub>)<sub>2</sub><sup>-</sup>), reacts with p-tolylazide to yield a dicopper complex with a symmetrically bridging 1,2,3-triazolide, [Cu<sub>2</sub>(μ-η<sup>1</sup>:η<sup>1</sup>-(1,4-bis(4-tolyl)-1,2,3-triazolide))DPFN]NTf<sub>2</sub>. This transformation exhibits bimolecular reaction kinetics and represents a key step in a proposed, bimetallic mechanism for copper-catalyzed azide-alkyne cycloaddition (CuAAC). The μ-alkynyl and μ-triazolide complexes undergo reversible redox events (by cyclic voltammetry), suggesting that a cycloaddition pathway involving mixed-valence dicopper species might also be possible. Synthesis and characterization of the mixed-valence μ-alkynyl dicopper complex, [Cu<sub>2</sub>(μ-η<sup>1</sup>:η<sup>1</sup>-C≡C(C<sub>6</sub>H<sub>4</sub>)CH<sub>3</sub>)DPFN](NTf<sub>2</sub>)<sub>2</sub>, revealed an electronic structure with an unexpected partially delocalized spin, as evidenced by electron paramagnetic resonance spectroscopy. Studies of the mixed-valence μ-alkynyl complex's reactivity suggest that a mixed-valence pathway is less likely than one involving intermediates with only copper(I).
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