The σ-donor properties of NHC ligands (NHC = N-heterocyclic carbene) are crucial in controlling their interaction with transition metals, and as a consequence, to determine the selectivity and reactivity of NHCs in transition-metal-catalysis. Herein, we report a simple NMR method for estimating the σ-donor properties of NHC ligands based on a straightforward ¹H NMR measurement of ligand precursors. We present evaluation of σ-donating properties for a range of NHC ligands varied by structure and electronics that are relevant to transition-metal-catalysis. We expect that the simple measurement of σ-donating properties of NHCs, together with the known methods for evaluating sterics and π-backbonding, will enhance the understanding of the properties of NHCs in transition-metal-catalysis.

NHC配体（NHC = N-杂环卡宾）的σ供体特性对于控制它们与过渡金属的相互作用至关重要，因此，对于确定过渡金属催化中NHC的选择性和反应性至关重要。本文中，我们报告了一种基于NMR配体前体的简单¹ H NMR测量，用于估算NHC配体的σ供体性质的简单NMR方法。我们目前对一系列与过渡金属催化有关的NHC配体的σ供体性质进行评估。我们希望，简单地测量NHC的σ供体性质，以及评估空间位和π反向键合的已知方法，将加深对NHC在过渡金属催化中的性质的了解。