title: "Hummingbird" behaviour of N-heterocyclic carbenes stabilises out-of-plane bonding of AuCl and CuCl units.
abstract: An N-heterocyclic carbene substituted by two expanded 9-ethyl-9-fluorenyl groups was shown to bind an AuCl unit in an unusual manner, namely with the AuX rod sitting out of the plane defined by the heterocyclic carbene unit. As shown by X-ray studies and DFT calculations, the observed large pitch angle (21°) arises from an easy displacement of the gold(I) atom away from the carbene lone-pair axis, combined with the stabilisation provided by weak CH⋅⋅⋅Au interactions involving aliphatic and aromatic H atoms of the NHC wingtips. Weak, intermolecular Cl⋅⋅⋅H bonds are likely to cooperate with the H⋅⋅⋅Au interactions to stabilise the out-of-plane conformation. A general belief until now was that tilt angles in NHC complexes arise mainly from steric effects within the first coordination sphere.
authors.affiliation: Laboratoire de chimie inorganique moléculaire et catalyse Institut de chimie UMR 7177 CNRS, Université de Strasbourg (France).
authors.forename: Matthieu
authors.initials: M
authors.lastname: Teci
authors.affiliation: Laboratoire de chimie inorganique moléculaire et catalyse Institut de chimie UMR 7177 CNRS, Université de Strasbourg (France). eric.brenner@unistra.fr.
authors.forename: Eric
authors.initials: E
authors.lastname: Brenner
authors.affiliation: Laboratoire de chimie inorganique moléculaire et catalyse Institut de chimie UMR 7177 CNRS, Université de Strasbourg (France). dmatt@unistra.fr.
authors.forename: Dominique
authors.initials: D
authors.lastname: Matt
authors.affiliation: Laboratoire de Chimie Quantique, Institut de chimie UMR 7177 CNRS, Université de Strasbourg 1 rue Blaise Pascal, 67008 Strasbourg (France).
authors.forename: Christophe
authors.initials: C
authors.lastname: Gourlaouen
authors.affiliation: Institut de Physique de Rennes, UMR 6251 CNRS, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes cedex (France).
authors.forename: Loic
authors.initials: L
authors.lastname: Toupet
keywords: N-heterocyclic carbenes; copper; density functional calculations; gold; hydrogen bonding; noncovalent interactions