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Updated: Feb 25, 2026

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C2-Symmetric Rhenacyclobutadienes: Key Intermediates in Re(V) Alkylidyne-Catalyzed Alkyne Metathesis Reactions
Long Yiu Tsang1, Mingxu Cui1, Lam Cheung Kong1
1Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong.
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Key rhenacyclobutadiene intermediates were isolated from the reactions of alkynes with a d2 Re(V) alkylidyne complex (5a) bearing bidentate phosphinoanilide ligands. Single crystal X-ray diffraction analysis revealed a pseudo-C2-symmetric structure wherein two phosphines are trans-oriented. These rhenacyclobutadienes can undergo [2 + 2] cycloreversion when treated with PMePh2 or another alkyne and are able to effect internal alkyne metathesis. This work represents the first observation of reversible [2 + 2] cycloaddition reactions of alkynes with a non-d0 alkylidyne complex, elucidates the mechanism of Re(V)-alkylidyne-catalyzed alkyne metathesis, and provides valuable insight for the rational design of new alkyne metathesis catalysts with improved activity based on non-d0 alkylidynes.
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