Azide alkyne cycloaddition facilitated by hexanuclear rhenium chalcogenide cluster complexes

Abstract

Two hexanuclear rhenium clusters containing azide ligands, [Re₆Se₈(PEt₃)₅(N₃)]BF₄ and [Re₆Se₈(PEt₃)₄(N₃)₂], were synthesized from the analogous pyridine complexes and fully characterized. Studies show that [Re₆Se₈(PEt₃)₅(N₃)]BF₄ reacts with activated alkynes, dimethyl acetylenedicarboxylate and methyl 4-hydroxyhex-2-yneoate, to form the triazolate cluster complexes [Re₆Se₈(PEt₃)₅(L1 or L2)]BF₄ (where L1 = 4,5-bis(methoxycarbonyl)-1,2,3-triazol-2-yl and L2 = 4-methoxycarbonyl-5-(1-propanol)-1,2,3-triazol-2-yl). The bis-triazolato complex, cis-[Re₆Se₈(PEt₃)₄(L1)₂] was also prepared via a similar reaction starting with cis-[Re₆Se₈(PEt₃)₄(N₃)₂] demonstrating that these clusters can promote two azide moieties to undergo heterocyclic ring formation. The structures of [Re₆Se₈(PEt₃)₅(N₃)]BF₄, [Re₆Se₈(PEt₃)₄(N₃)₂], and [Re₆Se₈(PEt₃)₅(L1)](BF₄), were determined by single-crystal X-ray diffraction analysis. In addition, studies involving the alkylation of [Re₆Se₈(PEt₃)₅(L1)]BF₄ with benzyl bromide and methyl iodide are reported.