1,2,4-triazol-3-ylidenes with an N-2,4-dinitrophenyl substituent as strongly π-accepting N-heterocyclic carbenes

Tetsuo Sato, Yoichi Hirose, Daisuke Yoshioka, Tsubasa Shimojo, Shuichi Oi

Research output: Contribution to journalArticlepeer-review

24 Citations (Scopus)

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 (ΔE bb) to the bond dissociation energies (BDE) of the Rh-C carbene 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 AuI complex resulted from the enhanced π acidity of the Au atom. π-Acidic carbene complexes: A series of Rh and Au complexes bearing 1,2,4-triazol-3- ylidenes with a N-2,4-dinitrophenyl (DNP) substituent were synthesised. Experimental and theoretical analyses revealed that these N-heterocyclic carbenes (NHCs) behave as strong π acceptors and weak σ donors, and the metal centers exibit enhanced π acidity compared to complexes with traditional σ-donating NHCs (see figure, EWG=electron withdrawing group).

Original languageEnglish
Pages (from-to)15710-15718
Number of pages9
JournalChemistry - A European Journal
Volume19
Issue number46
DOIs
Publication statusPublished - 2013 Nov 11

Keywords

  • acidity
  • carbene ligands
  • gold
  • ligand effects
  • rhodium

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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