Low-Coordinate W-W Quadruple Bond as an Alkene Surrogate: Divergent [2 + 2 + 2] and [2 + 2 + 1] Cycloadditions with Alkynes.
- 1Department of Chemistry, National Tsing Hua University, Hsinchu 30013, Taiwan.
Abstract
Although quadruply bonded metal-metal complexes constitute a large and well-established family, their cycloaddition chemistry remains underdeveloped because the quadruple bond is typically confined within a tetragonal, highly ligand-protected coordination environment. Herein, we demonstrate that a low-coordinate amidinate-supported W-W quadruple bond in W₂(μ-Cl)-(μ-κ²-Cl₂Li-(THF))-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂ behaves as an alkene surrogate in cycloaddition chemistry. Depending on ligand coordination, this W-W quadruple bond engages alkynes in either formal [2 + 2 + 2] or [2 + 2 + 1] pathways. In the absence of ancillary donor ligands, direct reaction with two alkynes proceeds through tail-to-tail [2 + 2 + 2] cycloaddition to afford C₄W₂ metallacycles, W₂Cl₂[μ-η²:η²-1,4-R₂C₄H₂]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂ (R = C₆H₅, 2-MeC₆H₄, 4-MeOC₆H₄, and n-C₃H₇), and a corresponding [2 + 2] intermediate, W₂Cl₂[μ-η²-2-MeC₆H₄CCH]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂, could be isolated and structurally characterized. In contrast, coordination of σ-donating ligands to the W-W core diverts the reaction pathway by stabilizing vinylidene intermediates, W₂Cl₂(C₅H₅N)-[μ-η¹:η²-CC-(H)-R¹]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂ (R¹ = 2-MeC₆H₄, t Bu, and SiMe₃), which subsequently react with a second alkyne (R²CCH) to furnish C₃W₂ ring products of the type W₂Cl₂[μ-η²:η²-1-R²-4-R¹H-C₄H]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂ bearing an exocyclic alkene fragment. In both [2 + 2 + 2] and [2 + 2 + 1] manifolds, while the initial cycloadducts adopt nonplanar conformations, sequential reduction populates the W-W δ manifold and drives planarization via δ-π conjugation between the W₂ unit and the organic fragment. Ultimately, the C₄W₂ systems are transformed into aromatic bimetallic metallabenzenes, [W₂(μ-κ²-1,4-R₂C₄H₂)-(μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂)₂] (R = C₆H₅, 2-MeC₆H₄, 3-MeC₆H₄, 4-MeC₆H₄, 4-MeOC₆H₄, 4-FC₆H₄, and n-C₃H₇), whereas the C₃W₂ system evolves into a bimetallic fulvene analogue, W₂Cl-[μ-κ²-1-C₆H₅-4- t BuH-C₄H]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂ and W₂(μ-H)-[μ-κ²-1-C₆H₅-4- t BuH-C₄H]-[μ-κ³-HC-(N-2,6- i Pr₂C₆H₃)-(N-2- i Pr-6-(C₃H₆)-C₆H₃)]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]. Taken together, these results expand the scope of cycloaddition partners to include a low-coordinate W-W quadruple bond.
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BibTeX
@article{chen2026lowcoordinate,
title = {{Low-Coordinate W-W Quadruple Bond as an Alkene Surrogate: Divergent [2 + 2 + 2] and [2 + 2 + 1] Cycloadditions with Alkynes.}},
author = {Wen-Chi Chen and Cian-Wei Yang and Bo-An Liao and Chiao-Yun Chen and Hong-Zhang Chen and Wen-Chuan Hsu and Yi-Chou Tsai},
journal = {JACS Au},
year = {2026},
month = sep,
doi = {10.1021/jacsau.6c01251},
url = {https://europepmc.org/article/MED/42953580},
note = {CC BY},
}
RIS
TY - JOUR
TI - Low-Coordinate W-W Quadruple Bond as an Alkene Surrogate: Divergent [2 + 2 + 2] and [2 + 2 + 1] Cycloadditions with Alkynes.
AU - Wen-Chi Chen
AU - Cian-Wei Yang
AU - Bo-An Liao
AU - Chiao-Yun Chen
AU - Hong-Zhang Chen
AU - Wen-Chuan Hsu
AU - Yi-Chou Tsai
PY - 2026
DA - 2026/09/24
JO - JACS Au
DO - 10.1021/jacsau.6c01251
UR - https://europepmc.org/article/MED/42953580
AB - Although quadruply bonded metal-metal complexes constitute a large and well-established family, their cycloaddition chemistry remains underdeveloped because the quadruple bond is typically confined within a tetragonal, highly ligand-protected coordination environment. Herein, we demonstrate that a low-coordinate amidinate-supported W-W quadruple bond in W₂(μ-Cl)-(μ-κ²-Cl₂Li-(THF))-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂ behaves as an alkene surrogate in cycloaddition chemistry. Depending on ligand coordination, this W-W quadruple bond engages alkynes in either formal [2 + 2 + 2] or [2 + 2 + 1] pathways. In the absence of ancillary donor ligands, direct reaction with two alkynes proceeds through tail-to-tail [2 + 2 + 2] cycloaddition to afford C₄W₂ metallacycles, W₂Cl₂[μ-η²:η²-1,4-R₂C₄H₂]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂ (R = C₆H₅, 2-MeC₆H₄, 4-MeOC₆H₄, and n-C₃H₇), and a corresponding [2 + 2] intermediate, W₂Cl₂[μ-η²-2-MeC₆H₄CCH]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂, could be isolated and structurally characterized. In contrast, coordination of σ-donating ligands to the W-W core diverts the reaction pathway by stabilizing vinylidene intermediates, W₂Cl₂(C₅H₅N)-[μ-η¹:η²-CC-(H)-R¹]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂ (R¹ = 2-MeC₆H₄, t Bu, and SiMe₃), which subsequently react with a second alkyne (R²CCH) to furnish C₃W₂ ring products of the type W₂Cl₂[μ-η²:η²-1-R²-4-R¹H-C₄H]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂ bearing an exocyclic alkene fragment. In both [2 + 2 + 2] and [2 + 2 + 1] manifolds, while the initial cycloadducts adopt nonplanar conformations, sequential reduction populates the W-W δ manifold and drives planarization via δ-π conjugation between the W₂ unit and the organic fragment. Ultimately, the C₄W₂ systems are transformed into aromatic bimetallic metallabenzenes, [W₂(μ-κ²-1,4-R₂C₄H₂)-(μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂)₂] (R = C₆H₅, 2-MeC₆H₄, 3-MeC₆H₄, 4-MeC₆H₄, 4-MeOC₆H₄, 4-FC₆H₄, and n-C₃H₇), whereas the C₃W₂ system evolves into a bimetallic fulvene analogue, W₂Cl-[μ-κ²-1-C₆H₅-4- t BuH-C₄H]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]₂ and W₂(μ-H)-[μ-κ²-1-C₆H₅-4- t BuH-C₄H]-[μ-κ³-HC-(N-2,6- i Pr₂C₆H₃)-(N-2- i Pr-6-(C₃H₆)-C₆H₃)]-[μ-κ²-HC-(N-2,6- i Pr₂C₆H₃)₂]. Taken together, these results expand the scope of cycloaddition partners to include a low-coordinate W-W quadruple bond.
SN - 2691-3704
ER -