“Hummingbird” Behaviour of N-Heterocyclic Carbenes Stabilises Out-of-Plane Bonding of AuCl and CuCl Units

Matthieu Teci (1) , Eric Brenner (1) , Dominique Matt (1) , Christophe Gourlaouen (2) , Loic Toupet (3)

1 Institut de Chimie de Strasbourg
2 Laboratoire de Chimie Quantique
3 IPR - Institut de Physique de Rennes

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

Keywords: Copper; Density functional calculations; gold; hydrogen bonding; N-heterocyclic carbenes; noncovalent interactions

Domains: Physics [physics]

Matthieu Teci, Eric Brenner, Dominique Matt, Christophe Gourlaouen, Loic Toupet. “Hummingbird” Behaviour of N-Heterocyclic Carbenes Stabilises Out-of-Plane Bonding of AuCl and CuCl Units. Chemistry - A European Journal, 2015, 21 (31), pp.10997--11000. ⟨10.1002/chem.201500840⟩. ⟨hal-01225625⟩