Relative Stability of Metal Complexes with Various Diene Ligands: Experimental and Computational Study

Abstract

The binding strength of various dienes was established by NMR investigation of ligand exchange reactions in (diene)Rh(acac) complexes. The binding affinity decreases in the following order: tetraphenyl-cyclopentadienone >1,5-cyclooctadiene > norbornadiene > tetrafluoro-benzobarrelene > dimethyl-tetrafluoro-benzobarrelene > bis(carboxymethyl)-norbornadiene ≫ bis(tert-butyl)-1,4-quinone >1,5-hexadiene > bis(carboxymethyl)-2,2,2-bicyclooctadiene > carvone >1,4-benzoquinone. The experimental data were used to validate the B97-3c method, which reproduces the observed trends with good accuracy (MAD = 1.1 kcal mol–1) and can be applied for rapid prediction of coordination strength. Computational screening of metal–diene combinations shows that the metal fragment has a larger impact on stability than the diene itself. In line with the Dewar–Chatt–Duncanson model, more electron-rich metals form more stable diene complexes. Electron-withdrawing cyclopentadienone and benzoquinone were identified as strong and effective ligands for further investigation in catalysis.