Correlating Electronic Properties of N‐Heterocyclic Carbenes with Structure, and the Implications of Using Different Probes

Abstract

AbstractThe σ‐donating and π‐accepting properties of a series of N‐methylimidazolium‐derived N‐heterocyclic carbenes, systematically altered at the 4,5‐positions, were determined using two NMR‐based probe techniques. The sterically slight methyl substituent provided reliable probe data, free from through‐space effects, and reliable measures of the electronic properties. Correlations with established electronic parameters for the substituents show that the electronic properties of carbenes, when extraneous effects are controlled for, are indeed predictable. These correlations were compared with earlier data which revealed a previously unrecognised systematic deviation for N‐aryl substituents.