Electron-donor/acceptor properties of carbynes, carbenes, vinylidenes, allenylidenes and alkynyls as measured by electrochemical ligand parameters

The bases of the main redox potential parameterization approaches and their extensions are reviewed with the methods to estimate the corresponding electrochemical ligand and metal center parameters. They are applied, in most cases for the first time, to series of carbyne, vinylidene, allenylidine and alkynyl complexes, allowing the estimate of the Pickett’s PL and Lever’s EL ligand parameters for quite a significant number (ca. 135) of ligands of these types which can then be ordered according to their net π-electron acceptor minus σ-donor character and compared with other ligands. The dependence of such parameters on the electronic properties of various groups and their transmission along the carbon skeleton of those ligands are illustrated and limitations and scopes of the parameterization approaches are discussed.