Issue 3, 2015

What can NMR spectroscopy of selenoureas and phosphinidenes teach us about the π-accepting abilities of N-heterocyclic carbenes?

Abstract

The electronic nature of the interaction of NHCs with metal centres is of interest when exploring their properties, how these properties influence those of metal complexes, and how these properties might depend on ligand structure. Selenourea and phosphinidene complexes have been proposed to allow the measurement of the π-accepting ability of NHCs, independent of their σ-donating ability, via the collection of 77Se or 31P NMR spectra, respectively. Herein, the synthesis and characterisation of selenoureas derived from a range of imidazol-2-ylidenes, 4,5-dihydroimidazol-2-ylidenes and triazol-2-ylidenes are documented. Computational studies are used to explore the link between the shielding of the selenium centre and the electronic properties of the NHCs. Results show that δSe is correlated to the energy gap between a filled lone pair orbital on Se and the empty π* orbital corresponding to the Se–NHC bond. Bond energy decomposition analysis indicated no correlation between the orbital σ-contribution to bonding and the chemical shielding, while a good correlation was found between the π-contribution to bonding and the chemical shielding, confirming that this technique is indeed able to quantify the ability of NHCs to accept π-electron density. Calculations conducted on phosphinidene adducts yielded similar results. With the link between δSe and δP and π-back bonding ability clearly established, these compounds represent useful ways in which to fully understand and quantify this aspect of the electronic properties of NHCs.

Graphical abstract: What can NMR spectroscopy of selenoureas and phosphinidenes teach us about the π-accepting abilities of N-heterocyclic carbenes?

Supplementary files

Article information

Article type
Edge Article
Submitted
24 Oct 2014
Accepted
31 Dec 2014
First published
02 Jan 2015
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2015,6, 1895-1904

Author version available

What can NMR spectroscopy of selenoureas and phosphinidenes teach us about the π-accepting abilities of N-heterocyclic carbenes?

S. V. C. Vummaleti, D. J. Nelson, A. Poater, A. Gómez-Suárez, D. B. Cordes, A. M. Z. Slawin, S. P. Nolan and L. Cavallo, Chem. Sci., 2015, 6, 1895 DOI: 10.1039/C4SC03264K

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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