π-face donation from the aromatic N-substituent of N-heterocyclic carbene ligands to metal and its role in catalysis

Raffaele Credendino, Laura Falivene, Luigi Cavallo

Research output: Contribution to journalArticlepeer-review

53 Scopus citations

Abstract

In this work, we calculate the redox potential in a series of Ir and Ru complexes bearing a N-heterocyclic carbene (NHC) ligand presenting different Y groups in the para position of the aromatic N-substituent. The calculated redox potentials excellently correlate with the experimental ΔE 1/2 potentials, offering a handle to rationalize the experimental findings. Analysis of the HOMO of the complexes before oxidation suggests that electron-donating Y groups destabilize the metal centered HOMO. Energy decomposition of the metal-NHC interaction indicates that electron-donating Y groups reinforce this interaction in the oxidized complexes. Analysis of the electron density in the reduced and oxidized states of representative complexes indicates a clear donation from the C ipso of the N-substituents to an empty d orbital on the metal. In case of the Ru complexes, this mechanism involves the Ru-alkylidene moiety. All of these results suggest that electron-donating Y groups render the aromatic N-substituent able to donate more density to electron-deficient metals through the C ipso atom. This conclusion suggests that electron-donating Y groups could stabilize higher oxidation states during catalysis. To test this hypothesis, we investigated the effect of differently donating Y groups in model reactions of Ru-catalyzed olefin metathesis and Pd-catalyzed C-C cross-coupling. Consistent with the experimental results, calculations indicate an easier reaction pathway if the N-substituent of the NHC ligand presents an electron-donating Y group. © 2012 American Chemical Society.
Original languageEnglish (US)
Pages (from-to)8127-8135
Number of pages9
JournalJournal of the American Chemical Society
Volume134
Issue number19
DOIs
StatePublished - May 4 2012

ASJC Scopus subject areas

  • Biochemistry
  • Colloid and Surface Chemistry
  • Chemistry(all)
  • Catalysis

Fingerprint

Dive into the research topics of 'π-face donation from the aromatic N-substituent of N-heterocyclic carbene ligands to metal and its role in catalysis'. Together they form a unique fingerprint.

Cite this