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

Abstract The 1 J CSe 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 1 J CSe values revealed a high donor capacity, very much in contrast to what the DFT‐calculated HOMO energies suggest. The 1 J CH coupling constants for the C‐2 atoms in azolium‐type NHC precursors were more readily obtained and show the same trend as the 1 J CSe coupling constants. In addition, the use of 77 Se 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 ( 77 Se) method in comparison with the Tolman electronic parameters derived from IR spectroscopy is demonstrated for the caffeine‐derived bis‐carbene 19 .