Hydrogen Bonds Dictate the Coordination Geometry of Copper: Characterization of a Square-Planar Copper(I) Complex

• Published in: Angewandte Chemie International Edition 2016-02, Vol.55 (9), p.3101-3105
• Main Authors: Dahl, Eric W., Szymczak, Nathaniel K.
• Format: Article
• Language: English
• Subjects: Bonding; Coordination compounds; Copper; Copper - chemistry; Crystallography, X-Ray; Electron transfer; entatic state; Geometric constraints; Geometry; Hydrogen; Hydrogen Bonding; Hydrogen bonds; Molecular Structure; Proteins; secondary coordination sphere; Spectrophotometry, Ultraviolet; Spectroscopy, Near-Infrared; square-planar complexes; Strength
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201511527

6,6′′‐Bis(2,4,6‐trimethylanilido)terpyridine (H2TpyNMes) was prepared as a rigid, tridentate pincer ligand containing pendent anilines as hydrogen bond donor groups in the secondary coordination sphere. The coordination geometry of (H2TpyNMes)copper(I)‐halide (Cl, Br and I) complexes is dictated by the strength of the NH–halide hydrogen bond. The CuICl and CuIICl complexes are nearly isostructural, the former presenting a highly unusual square‐planar geometry about CuI. The geometric constraints provided by secondary interactions are reminiscent of blue copper proteins where a constrained geometry, or entatic state, allows for extremely rapid CuI/CuII electron‐transfer self‐exchange rates. Cu(H2TpyNMes)Cl shows similar fast electron transfer (≈105 m−1 s−1) which is the same order of magnitude as biological systems. Entatic state: Hydrogen bonds constrain the geometry of CuI and CuII complexes. A highly unusual square‐planar geometry about CuI (see structure) is shown to be nearly isostructural to the CuII core. The minimal reorganization energy between redox states allows for extremely rapid CuI/CuII electron‐transfer self‐exchange rates.