Expanding the Redox Chemistry of Yttrium, the Lanthanides, and Uranium through Synthesis and Reactivity of Bis-, Tris-, and Tetrakis-(Trimethylsilylcyclopentadienyl) Complexes

This dissertation focuses on the synthesis, characterization, and reactivity of unique organometallic complexes of yttrium, the lanthanides, and uranium in efforts to expand the limits of known redox chemistry of these elements. The results in this dissertation arose from investigations of previously established reduction reactions involving these metal ions that were not fully understood. In general, rare metal and actinide complexes of formula A 3M and A2A'M (A = substituted cyclopentadienyl; A' = different monoanionic ligand; M = yttrium, lanthanide, uranium) were reacted with a variety of bases, alkyllithium reagents, azides, and alkali metals under different conditions. These investigations led to several new examples of substrate reduction and small molecule activation, and in some cases, gave insight into how these complicated reduction processes might be occurring. In the course of these studies, eight new oxidation states were discovered: the first examples of molecular complexes of the following ions, Y2+, Ho 2+, Er2+, Tb2+, Pr2+, Gd2+, Lu2+, and U2+.;Chapter 1 describes the reactivity of the unsolvated metallocene tetraphenylborate complexes, [(C5Me5)2Ln][(mu-Ph)2BPh 2] (Ln = Y, Sm) with reagents that have previously been reduced by rare earth or uranium complexes.;Chapter 2 focuses on an expansion of these reactivity studies in which the yttrium tetraphenylborate complex [(C5Me5) 2Y][(mu-Ph)2BPh2] reacted with LiEt to form an unexpected unsolvated ethyl complex, (C5Me5) 2YEt.;In Chapter 3, efforts to isolate a molecular complex of Y2+ for the first time are described.;Chapter 4 describes how the method of reduction used to isolate the 4d 1 Y2+ complex was applied to generate the first molecular complexes of Ho2+ and Er2+.;In anticipation that even more new Ln2+ ions might be obtainable from the reduction of Ln3+ compounds containing these ligands, the synthesis of other (C5H4SiMe 3)3Ln compounds was required. Chapter 5 details the methods required to obtain these compounds for Ln = La and Lu, the largest and smallest lanthanides.;In Chapter 6, the first isolation of the Tb2+ ion in molecules is described.;In Chapter 7, the reactivity of the Y2+ complexes, [(18-crown-6)K][(C 5H4SiMe3)3Y] and [K(2.2.2-cryptand)][(C 5H4SiMe3)3Y] were examined with N 2 and naphthalene.;The available oxidation states for uranium, a much more heavily studied metal, are widely accepted and documented to be +3, +4, +5, and +6. Chapter 8 reveals that the method of potassium reduction of Ln3+ in the presence of 2.2.2-cryptand could be applied to uranium, and the first evidence of isolable molecular U2+ is discussed.;Chapter 9 discusses the complex nature of the reaction between the U 2+ complex, [K(2.2.2-cryptand)][(C5H4SiMe 3)3U], and cyclooctatetraene. Evidence for the formation of uranocene, (C8H8)2U, as well as other U3+ and U4+ complexes is presented.;Once it was established that Ln2+ complexes can be isolated for all the lanthanide elements (except for Pm, which is radioactive), attempts to make the (C5H4SiMe3)3Ln and [K(2.2.2-cryptand)][(C5H4SiMe3)3Ln] complexes with the traditional previously known divalent lanthanide ions were carried out to make a direct comparison between the new 4fn5d 1 ions and the traditional divalent ions that have historically been considered to have 4fn+1 configurations. Chapter 10 explains the synthetic variations required to isolate these other analogs and a library of directly comparable Ln3+ vs Ln2+ complexes is presented. (Abstract shortened by UMI.).