| Popis: |
Thermochemical cycles that incorporate electrode potential data have emerged as a powerful approach to extract bond energy data that are frequently not directly available by other experimental methods. Cyclic voltammetry (CV) is the most commonly used technique; its transient nature offers the advantage that bonding energetics can be investigated even for short-lived species. The reliability of the extracted bond energies depends on the accuracy of the electrode potential data that are used. The CV technique is briefly discussed with focus on simple but very important issues that frequently lead to inconsistencies in published electrode potential data. The use of thermochemical cycles for quantitative measurements of bond energies in organometallic complexes is discussed and comprehensive lists of derived bond energy data are presented. Particular emphasis is given to metal–hydride bond strengths with respect to dissociation of the hydride ligand as a proton (M–H acidity, pKa), as a hydrogen atom (M–H homolytic bond dissociation energies (BDEs)), or as a hydride (M–H hydricity). Furthermore, determinations of M–M bond energies and homolytic and heterolytic bond energies of C–H bonds in π-coordinated and σ-coordinated ligands are included. The consequences of one-electron redox processes on homolytic and heterolytic M–H, M–X, and ligand C–H bond strengths are quantified. Square schemes that yield thermodynamic data for redox-induced structural change or isomerization processes are briefly discussed. Finally, recent, selected applications where the thermodynamic data have played an interesting role in reactivity studies are highlighted. |
