Piano-stool iron(ii) complexes as probes for the bonding of n-heterocyclic carbenes: indications for -acceptor ability

Mercs, Laszlo; Labat, Gaël; Neels, Antonia; Ehlers, Andreas; Albrecht, Martin

doi:10.1021/om060637c

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Piano-stool iron(ii) complexes as probes for the bonding of n-heterocyclic carbenes: indications for -acceptor ability

Mercs, Laszlo Department of Chemistry, University of Fribourg, Switzerland
Labat, Gaël Institute of Microtechnology, University of Neuchâtel, Switzerland
Neels, Antonia Institute of Microtechnology, University of Neuchâtel, Switzerland
Ehlers, Andreas Scheikundig Laboratorium, Vrije Universiteit van Amsterdam, The Netherlands
Albrecht, Martin Department of Chemistry, University of Fribourg, Switzerland

12.10.2006

Published in:

Organometallics. - 2006, vol. 25, no. 23, p. 5648 -5656

English A series of new piano-stool iron(II) complexes comprising mono- and bidentate chelating N-heterocyclic carbene ligands [Fe(cp)(CO)(NHC)(L)]X have been prepared and analyzed by spectroscopic, electrochemical, crystallographic, and theoretical methods. Selectively substituting the L site with a series of ligands going from carbene to pyridine to CO suggests that CO is the strongest π acceptor, while the behavior of pyridine and carbene is nearly identical. This suggests that in these complexes comprising an electron-rich iron(cp)(carbene) fragment, N-heterocyclic carbenes are not pure σ donors but also moderate π acceptors. Theoretical calculations support this bonding model and indicate charge saturation at the metal as key for π back-bonding to N-heterocyclic carbenes. On the basis of voltammetric measurements, the Lever electrochemical parameter of these carbenes has been determined: E_L = +0.29. Systematic substitution of the wingtip groups of the carbene revealed only subtle changes in the electronic properties of the iron center, thus providing a suitable methodology for ligand-induced fine-tuning of the coordinated metal.

Faculty

Faculté des sciences et de médecine

Department

Département de Chimie

Language