Aggregation of Zintl Ions

The primary intent of this dissertation is to develop strategies to aggregate Zintl ions containing transition metal fragments and/or atoms. Development for such an endeavor began in the following manner: (1) identifying similarities with other fields of chemistry wherein successful aggregation was carried out (2) identifying suitable transition metal containing Zintl clusters as precursors for aggregation (3) combining both suitable materials and already published techniques to aggregate Zintl clusters (4) further improving the synthetic approaches presented to address the pitfalls in these syntheses. These steps will be covered in detail throughout this dissertation.

After introducing the fundamentals of Zintl chemistry, noble metal aggregation, and ligand protected clusters (Chapter 1), the first attempt at aggregation using oxidation by solvent is presented (Chapter 2). Using solely solvent oxidation, in this case pyridine, in the presence of a transition metal fragment, Cr(CO)₃, results in the isolation of the [Bi₇]^3– anion. Although the resulting anion did not contain a transition metal fragment, the solvent caused oxidation from its [Bi₂]^2– parent, to generate a naked aggregated anion.

Following this result, we looked to applying noble metal aggregation approaches to transition metal-Zintl clusters containing carbonyl ligands. Using transition metal rich clusters as [Bi₃Ni₄(CO)₆]^3–, we demonstrate the same approaches are applicable to Zintl chemistry by generating the [Bi₁₂Ni₇(CO)₄]^4– intermetalloid anion (Chapter 3). Furthermore, the species is unique in that it strongly resembles condensed polyhedra seen in transition metal clusters. The implications of this are discussed and the electronic structure elucidated.

We further applied the noble metal aggregation approach to clusters deficient in carbonyl ligands. Using this time [Ni@Sn₉Ni(CO)]^3– as a starting material we isolate the novel fused cluster as [Sn₁₄Ni(CO)]^4– (Chapter 4). Unlike the previous Bi/Ni species, the [Sn₁₄Ni(CO)]^4– anion is rationalized using modified Wades-Mingos rules for cluster bonding. It is also an educational example the differences that occur between the cluster bonding counts and cluster valence counts once clusters enlarge beyond spherical shapes.

Chapter 5, address the pitfalls of using naked clusters for aggregation by introducing the new developing field of ligand protected-Zintl clusters generated from heterogeneous reactions. The breadth of knowledge is further expanded by using stannyl-halides to generate tri-substituted germanium clusters as [Ge₉{SnR₃}₃]^– (R= ⁱPr, Cy). These tri-substituted clusters are used as precursors to generate larger assemblies with the use of transition metals, Pd(PPh₃)₄ in this case. The generated [Ge₁₈Pd₃{ER}₆]^2– (ER=SnⁱPr₃, SnCy₃, SiⁱPr₃) “twinned icosahedra”, contains a novel architecture and unique electronic structure. Furthermore, the nature of the bound substituent in [Ge₁₈Pd₃{ER}₆] (ER=SnⁱPr₃, SnCy₃, SiⁱPr₃) moieties can lead to positional isomerism that has not been observed before in main group deltahedral clusters. The phenomena observed between case are elucidated and rationalized.

Chapter 6, describes the further reactivity of both transition metal carbonyl and hypersilyl ligated Zintl clusters. The reactions conducted, demonstrate that both types of clusters have unexplored reactivity and that modern organometallic synthetic approaches can be applied to them. This avenue of research holds great promise for further exploration.

Lastly, this tome ends with a summary and discussion of possible avenues of research. Primarily focused on the generation of larger assemblies and exploration of different ligands for use in heterogeneous reactions.