Work

N -Heterocyclic Carbene-Carbodiimide (NHC-CDI) Adducts: A Systematic Investigation of Electronic Modifications on Kinetic and Thermodynamic Properties of Adduct Association and Dissociation

Year: 2025

Type: article

Abstract: N -Heterocyclic carbene-carbodiimide (NHC-CDI) adducts are versatile compounds that can be used as ligands and (pre)catalysts, but their systematic structure–property relationships are underexplored. Herein, we investigated how structural electronic variations on both the NHC and CDI affect the inherent kinetic and thermodynamic properties of the adducts. Using in situ carbene trapping and variable-temperature NMR spectroscopy, we measured the rates of dissociation and the equilibrium constants and then used Eyring and van’t Hoff analyses to calculate Δ G ‡ and Δ G, respectively. Linear free-energy relationships indicate that changing the para position of the CDI substituents yields a similar effect to changing the NHC core. These CDI structural modifications affected the adducts’ thermodynamics (Δ G ) more than the kinetics (Δ G ‡ ) and were found to be influenced more by inductive, rather than resonance, factors. Preliminary results suggest a steric threshold beyond which steric effects dominate electronic effects in governing the strength of the adduct bond. This systematic investigation provides valuable insight into the design of NHC-CDIs for current and future applications.

Source: The Journal of Organic Chemistry

DOI: 10.1021/acs.joc.5c00225

Authors: Le Dung Pham, Briana Krupinsky, Anthony W. Schlimgen, Jessica R. Lamb

Institution: University of Minnesota

Language: English

Topic: N-Heterocyclic Carbenes in Organic and Inorganic Chemistry

Subfield: Organic Chemistry

Field: Chemistry

Domain: Physical Sciences

Open Access status: green