Synthesis and dynamic behaviour of zwitterionic [M(η6-C6H5-BPh3)(coe)2] (M = Rh, Ir) cyclooctene complexes

Abstract

The synthesis and structural characterization of zwitterionic [(η⁶-C₆H₅-BPh₃)M(coe)₂] (M = Rh, Ir) cyclooctene complexes is described. Both complexes exhibit an unusual exo–endo conformation of both cyclooctene ligands in the solid state. However, an equilibrium between the endo–endo and exo–endo rotational isomers arising from the hindered rotation about the metal–cyclooctene bond is observed in solution. Rotational barriers of around 65 kJ mol⁻¹ (Rh) and 84 kJ mol⁻¹ (Ir) have been determined by 2D EXSY NMR spectroscopy. The rotation process has also been studied by DFT calculations that showed that the dynamic behaviour is a consequence of the oscillation of the cyclooctene ligands about the metal–olefin bond instead of completing a full rotation.