C-13 NMR Spectroscopy of N-Heterocyclic Carbenes Can Selectively Probe sigma Donation in Gold(I) Complexes

Demian Marchione, Maria A. Izquierdo, Giovanni Bistoni, Remco W. A. Havenith, Alceo Macchioni, Daniele Zuccaccia, Francesco Tarantelli, Leonardo Belpassi

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Abstract

The Dewar-Chatt-Duncanson (DCD) model provides a successful theoretical framework to describe the nature of the chemical bond in transition-metal compounds and is especially useful in structural chemistry and catalysis. However, how to actually measure its constituents (substrate- to-metal donation and metal-to-substrate back-donation) is yet uncertain. Recently, we demonstrated that the DCD components can be neatly disentangled and the pi back-donation component put in strict correlation with some experimental observables. In the present work we make a further crucial step forward, showing that, in a large set of charged and neutral N-heterocyclic carbene complexes of gold(I), a specific component of the NMR chemical shift tensor of the carbenic carbon provides a selective measure of the sigma donation. This work opens the possibility of 1) to characterize unambiguously the electronic structure of a metal fragment (LAu(In+/0 in this case) by actually measuring its sigma-withdrawing ability, 2) to quickly establish a comparative trend for the ligand trans effect, and 3) to achieve a more rigorous control of the ligand electronic effect, which is a key aspect for the design of new catalysts and metal complexes.

Original languageEnglish
Pages (from-to)2722-2728
Number of pages7
JournalChemistry
Volume23
Issue number11
DOIs
Publication statusPublished - Feb-2017

Keywords

  • bond theory
  • gold
  • N-heterocyclic carbenes
  • NMR spectroscopy
  • TRANSITION-METAL-COMPLEXES
  • DENSITY-FUNCTIONAL THEORY
  • ELECTROCHEMICAL PARAMETRIZATION
  • CHEMICAL-SHIFTS
  • BACK-DONATION
  • LIGAND
  • BOND
  • CATALYSIS
  • APPROXIMATION
  • CHARACTER

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