Rhodium and Palladium Complexes of N‑Heterocyclic Olefin (NHO) Ligand Fused with the 9,10-Dihydro-9,10-ethanoanthracene Framework

A saturated
type of N-heterocyclic olefin (NHO) was synthesized
by fusing 2-methyleneimidazolidine with a 9,10-dihydro-9,10-ethanoanthracene
framework, and rhodium and palladium complexes with this NHO were
successfully obtained. The Tolman electronic parameter (TEP) value
calculated using the Rh complex indicated that the electron-donating
ability of the present saturated NHO was weaker than those of unsaturated
NHOs. X-ray diffraction (XRD) studies of three Pd complexes confirmed
that these complexes were [(NHO)­PdCl­(μ-Cl)]2, trans-[(NHO)2PdCl2], and cis-[(NHO)2PdCl2]. trans-[(NHO)2PdCl2] isomerized to a cis-complex
in an acetonitrile solution. Furthermore, our computational studies
indicated that the N-substituent is crucial for the planarity of the
2-methyleneimidazolidine moiety of our NHO and its metal complexes.