title: 1,2,4-Triazol-3-ylidenes with an N-2,4-dinitrophenyl substituent as strongly π-accepting N-heterocyclic carbenes.
abstract: The synthesis and characterisation of a series of new Rh and Au complexes bearing 1,2,4-triazol-3-ylidenes with a N-2,4-dinitrophenyl (N-DNP) substituent are described. IR, NMR, single-crystal X-ray diffraction and computational analyses of the Rh complexes revealed that the N-heterocyclic carbenes (NHCs) behaved as strong π acceptors and weak σ donors. In particular, a natural bond orbital (NBO) analysis revealed that the contributions of the Rh→Ccarbene π backbonding interaction energies (ΔEbb ) to the bond dissociation energies (BDE) of the RhCcarbene bond for [RhCl(NHC)(cod)] (cod=1,5-cyclooctadiene) reached up to 63 %. The Au complex exhibited superior catalytic activity in the intermolecular hydroalkoxylation of cyclohexene with 2-methoxyethanol. The NBO analysis suggested that the high catalytic activity of the Au(I) complex resulted from the enhanced π acidity of the Au atom.
authors.affiliation: Department of Applied Chemistry, Graduate School of Engineering, Tohoku University, 6-6-11 Aramaki-Aoba, Aoba-ku, Sendai 980-8579 (Japan), Fax: (+81) 22-795-5874; Environment Conservation Research Institute, Tohoku University, 6-6-11 Aramaki-Aoba, Aoba-ku, Sendai 980-8579 (Japan). tetsuo@aporg.che.tohoku.ac.jp.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Sato
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Hirose
authors.forename: Daisuke
authors.initials: D
authors.lastname: Yoshioka
authors.forename: Tsubasa
authors.initials: T
authors.lastname: Shimojo
authors.forename: Shuichi
authors.initials: S
authors.lastname: Oi
keywords: acidity; carbene ligands; gold; ligand effects; rhodium