Since the discovery of ferrocene six decades ago, organometallic chemistry has provided an extensive series of breakthroughs that have advanced science and technology in many areas. One of the key ligands that has supported this development is the cyclopentadienyl ligand. From the early involvement of C5H5 in the discovery of metallocenes to more recent highly-substituted variants that lead to sophisticated catalysts, the cyclopentadienyl ligand has been of central importance in organometallic chemistry. Although efforts have been made to go beyond cyclopentadienyl ligands in the “post-metallocene era,” cyclopentadienyl ligands still continue to make significant contributions. This talk will illustrate another type of chemical advancement accessible using the cyclopentadienyl ligand: the discovery of new oxidation states in the periodic table. A fundamental aspect of the chemistry of any element is the number of formal oxidation states available in molecules for chemical reactions. The range of accessible oxidation states for all of the elements has been continuously tested for decades and the boundaries were thought to be well-established across the periodic table. However, recently the special environment provided by three silyl-substituted cyclopentadienyl ligands has led to the discovery of the first examples of formal +2 oxidation states in molecular complexes of yttrium, holmium, erbium, praseodymium, gadolinium, terbium, lutetium, uranium, and thorium. The synthesis, structure, and physical properties of these complexes will be described as well as their reactivity. The implications of this organometallic approach for increasing the range of oxidation states accessible in molecular complexes will be discussed.

Award Address (ACS Award in Organometallic Chemistry sponsored by the Dow Chemical Co. Foundation). Importance of organometallic chemistry in the discovery of new oxidation states of the rare earth and actinide elements in molecular complexes

249th National Meeting (2015)

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