Determining the Ligand Properties of N‐Heterocyclic Carbenes from 77Se NMR Parameters

Abstract

AbstractThe 1JCSe coupling constants for a range of NHC–selenium adducts have been measured and used to establish a correlation with the σ‐donor strength of the respective carbenes. For the subclass of amido‐carbenes, the 1JCSe values revealed a high donor capacity, very much in contrast to what the DFT‐calculated HOMO energies suggest. The 1JCH coupling constants for the C‐2 atoms in azolium‐type NHC precursors were more readily obtained and show the same trend as the 1JCSe coupling constants. In addition, the use of 77Se chemical shifts to determine π‐acidity has been extended to a broader range of derivatives, namely 1·Se–22·Se. The superior resolution of the δ(77Se) method in comparison with the Tolman electronic parameters derived from IR spectroscopy is demonstrated for the caffeine‐derived bis‐carbene 19.