Charge-transfer bonding in metal–arene coordination

• Published in: Coordination chemistry reviews 2000-05, Vol.200, p.831-873
• Main Authors: Hubig, Stephan M, Lindeman, Sergey V, Kochi, Jay K
• Format: Article
• Language: English
• Subjects: Charge-transfer bonding; CH bond activation; Donor–acceptor complex; Electrophilic–nucleophilic umpolung; Metal–arene coordination; X-ray structures
• ISSN: 0010-8545; 1873-3840
• DOI: 10.1016/S0010-8545(00)00322-2

X-ray crystallographic structures of donor–acceptor complexes of aromatic hydrocarbons with transition metals are re-examined with the focus on the arene ligands. Thus, significant structural and electronic changes are revealed in the arene moiety due to coordination to the metal center including: (i) expansion of the aromatic six-carbon ring; (ii) endocyclic π-bond localization; (iii) distortion of the planarity (folding) of the arene ring; and (iv) shortening of the metalarene bond distances. All structural features are characteristic of metal–arene (π- or σ-) complexes that exhibit various degrees of (metal-to-ligand) charge transfer. The concept of charge-transfer bonding not only explains the structural details but also the various facets of chemical reactivity of metal-coordinated arenes including efficient carbonhydrogen bond activation and nucleophilic–electrophilic umpolung, both of which are critical factors in homogeneous metal catalysis.