Studies on the Effect of Positive and Negative Charges on the ⁷⁷Se NMR Shifts of Selenones and Selenenyls of N-heterocyclic Carbenes of Imidazolium-4,5-dicarboxylates

The Journal of Organic Chemistry, Journal Year: 2025, Volume and Issue: unknown

Published: Feb. 4, 2025

1,3-Imidazole-4,5-dicarboxylic acid derivatives were investigated with respect to the properties of underlying N-heterocyclic carbenes. Their selenium adducts prepared as diesters, monoesters, and dianionic dicarboxylates. Se-methylation yielded selenenyls (cationic selenoethers). 77Se NMR shifts are considered a measure electronic carbene. Since they very sensitive external (solvent, pH, temperature, reference reagent, method) internal parameters (substituent effects, steric nonclassical H-bonding, anisotropy), difficulties can arise in reliably interpreting these values. Our model compounds allow systematic investigation influence charges on since both structural changes measurement conditions have been minimized. Depending charge, cover range from 42.1 ppm (dianionic dicarboxylate) via 65.0 (monoanionic 92.5 (neutral diester) 153.8 selenoether) DMSO-d6. The signals also show considerable solvent pH dependence, which was selection solvents (MeOD, CDCl3, CD2Cl2, CD3COOD, CD3CN, acetone-d6, THF-d8, pyridine-d5, toluene-d8, DMSO-d6) values D2O. Linear relationships found between HOMO LUMO energies shifts, respectively.

Language: Английский

77Se NMR spectroscopy of selenium adducts of N-heterocyclic carbenes

Advances in heterocyclic chemistry, Journal Year: 2024, Volume and Issue: unknown

Published: Jan. 1, 2024

Language: Английский