σ-π Continuum in Indole-Palladium(II) Complexes

• Published in: Angewandte Chemie International Edition 2016-04, Vol.55 (17), p.5322-5326
• Main Authors: Yamamoto, Koji, Kimura, Seita, Murahashi, Tetsuro
• Format: Article
• Language: English
• Subjects: indoles; palladium; π-complexes; σ-complexes; σ-π continuum
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201601992

The intrinsic features of (hetero‐arene)–metal interactions have been elusive mainly because the systematic structure analysis of non‐anchored hetero‐arene–metal complexes has been hampered by their labile nature. We report successful isolation and systematic structure analysis of a series of non‐anchored indole–palladium(II) complexes. It was revealed that there is a σ–π continuum for the indole–metal interaction, while it has been thought that the dominant coordination mode of indole to a metal center is the Wheland‐intermediate‐type σ‐mode in light of the seemingly strong electron‐donating ability of indole. Several factors which affect the σ‐ or π‐character of indole–metal interactions are discussed. Continuum split: The isolation and systematic structural analysis of non‐anchored indole–palladium(II) complexes revealed that there is a σ–π continuum for heteroarene–metal complexes. These findings may provide insights into key catalytic intermediates of metal‐catalyzed heteroarene transformations.