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Updated: Jan 18, 2026
19:58
Palladium N-Heterocyclic Carbene Complexes: Synthesis from Benzimidazolium Salts and Catalytic Activity in Carbon-carbon Bond-forming Reactions
Published on: July 30, 2017
10.2K
Bidentate Phosphine Ligand Impacts on Previously Inaccessible 5-Membered N-Heteroaryne Formation and
Erin E Plasek1, Roman G Belli1, Douglas M Kavaguti1
1University of Minnesota, Minneapolis, MN 55455 USA.
Organometallics
|September 8, 2025
Summary
Researchers explored nickel-stabilized N-heteroarynes, finding that specific phosphine ligands with alkyl substituents and short linkers enable their formation and enhance reactivity in coupling reactions.
Area of Science:
- Organometallic Chemistry
- Synthetic Organic Chemistry
Background:
- 5-Membered N-heteroarynes were previously considered synthetically challenging to access.
- Recent advancements utilized bisphosphine-ligated nickel centers to stabilize these intermediates.
Purpose of the Study:
- To investigate the influence of ancillary phosphine ligands on the formation and reactivity of 5-membered N-heteroarynes.
- To identify optimal ligand structural features for successful N-heteroaryne synthesis.
Main Methods:
- Synthesis and characterization of four bidentate phosphine ligands with varied substituents and backbone lengths.
- Evaluation of these ligands in nickel-catalyzed N-heteroaryne formation.
- Reactivity studies using 2-PyZnBr as a nucleophilic coupling partner.
- Crystallographic analysis of resulting nickel-aryne complexes.
Main Results:
- Ligands with phenyl phosphine substituents or linker lengths exceeding three carbons were ineffective.
- Alkyl phosphine substituents with one, two, or three carbon linkers facilitated N-heteroaryne formation.
- Altered linker lengths significantly enhanced regioselectivity in coupling reactions (up to >20:1 ratio).
Conclusions:
- The structural features of ancillary phosphine ligands critically control the formation and reactivity of nickel-stabilized 5-membered N-heteroarynes.
- Ligand backbone length plays a key role in achieving high regioselectivity in subsequent coupling reactions.
- Crystallographic data supports the hypothesis that structural differences in Ni-aryne complexes influence regioselectivity.
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