ORGANOMETALLIC IONS AND ION-PAIRS

This chapter focuses on organometallic ions and ion pairs. The contrasting descriptions have also been applied to organometallic cations as electrophiles and oxidants in reference to their electron acceptor behavior, as the direct comparison are described in the chapter. The electron-donor property of an organometallic reagent, as indicated by the vertical ionization potential (IP), is strongly dependent on the ligands. For example, changing a methyl ligand to ethyl is sufficient to increase the donor property by almost 12 kcal/mol. The contact ion pairs are often visually apparent by their colors and are unequivocally detected by the appearance of new absorption bands in the electronic spectra. They are strongly influenced by polar solvents, and they are subject to special salt effects. The chemical activation of contact ion pairs to geminate radical pairs by electron transfer is photochemically effected by the deliberate irradiation of the charge-transfer absorption band. Nucleophiles are often most effective as the negatively charged anions, and they are also referred to as “Brernsted and Lewis bases” or in terms of their softness on the hard and soft acid-base (HSAB) scale. © 1991 Academic Press, Inc.