A unified ligand electronic parameter based on 13C NMR spectroscopy of N-heterocyclic carbene complexes

The donor strengths of various mono- and bidentate ligands can be easily compared on a unified 13C NMR spectroscopic scale.

Generalization of the Tolman electronic parameter: the metal–ligand electronic parameter and the intrinsic strength of the metal–ligand bond

The MLEP is a new, generally applicable measure of the metal–ligand bond strength based on vibrational spectroscopy, replacing the TEP.

Electronic Influence of Different β-Diketonato Ligands on the Electrochemical Behaviour of Tris(β-Diketonato)M(III) Complexes, M = Cr, Mn and Fe

The reduction of the MIII/MII metal couple of complexes Cr (β-diketonato)3, Fe (β-diketonato)3 and Mn (β-diketonato)3 is reviewed and compared. The ease of reduction of the MIII/MII couple of M(β-diketonato)3 complexes increases according to the metal sequence Cr (β-diketonato)3 < Fe (β-diketonato)3 < Mn (β-diketonato)3 (with the most positive reduction potential). Good linear relationships obtained between the reduction potential and different electronic parameters related to the β-diketonato ligand on these MIII(β-diketonato)3 complexes, show that the ease of reduction of the MIII/MII couple increases with decreasing acidic strength (pKa) of the respective β-diketone ligands. It also increases with increasing total group electronegativity of the R and R' groups on the respective β-diketonato ligand (RCOCHCOR')− of the M(β-diketonato)3 complexes, (χR + χR'), as well as with an increase in the total Hammett sigma meta constants (σR + σR'), and also with increasing value of the Lever ligand electronic parameter (EL) of ligand (RCOCHCOR')−.

Relationship of QTAIM and NOCV Descriptors with Tolman’s Electronic Parameter

The σ-donor properties of various P-donor ligands have been studied at the PBEPBE level of theory, which has proved to be accurate in computing the symmetric carbonyl stretching frequencies in nickel(0)-tricarbonyl complexes containing P-donor ligands. The delocalization index from the QTAIM methodology and the energy component associated with the NOCV deformation density representing the donor interaction give the best correlation with Tolman’s electronic parameters, whereas the electron density at the bond critical point and the Wiberg bond index are connected with the donor strength of the ligands to a lesser extent.