Diverse Reactivity of Rhenium β-Diketiminates

Chapter 1. Previous work with group 5 imido β-diketiminates and rhenium terminal oxo complexes is summarized, which in combination provide the theoretical basis for the subsequent chapters. The overarching hypothesis and goals of this work are stated.Chapter 2. Synthetic access to the first rhenium oxo β-diketiminate is achieved. Subsequently, the oxygen atom transfer (OAT) reactivity of this complex is gauged. It is determined that OAT from this complex is limited to trialkylphosphines of a moderate steric profile (e.g. PEt3), as small trialkylphosphines (e.g. PMe3) bind strongly to the metal center, and larger phosphines (e.g. PPh3) are kinetically limited due to the encumbering β-diketiminate ligand. Nitrene transfer from the β-diketiminate ligand to the metal is also observed, implying an ancillary limitation of this ligand in low valent rhenium complexes at high temperatures.Chapter 3. Attempts to incorporate a cyclopentadienyl ligand into the rhenium oxo β-diketiminate system using NaCp led to the isolation of an olefin-supported rhenium(III) terminal oxo complex. It was found that using SnCp2 rather than NaCp leads to the intended rhenium(V) oxo Cp complex. The reactivity of this rhenium(V) complex suggested that both the Cp ligand and oxo ligand are susceptible to nucleophilic attack, yielding a variety of rhenium(III) complexes. Computational studies suggest some degree of metal-ligand conjugation (“π-loading”) exists between the Cp and oxo ligands in the starting rhenium(V) complex, which supports the observations made during reactivity studies.Chapter 4. The oxygen atom transfer reactivity of a rhenium(III) terminal oxo β-diketiminate complex is evaluated. It is shown that this compound will only transfer its oxo ligand to electrophilic reagents (e.g. isocyanides and CO) rather than nucleophilic ones (e.g. PMe3). A number of rhenium(I) isocyanide and carbonyl complexes are isolated as products of the oxygen atom transfer process. In all, the results suggest that the oxo moiety of the starting rhenium(III) complex behaves as a nucleophile, and has no demonstrable electrophilic character.Chapter 5. Reduction of a cationic rhenium(V) oxo Cp β-diketiminate with metallic sodium yields an anionic rhenium(I) complex that is both strongly reducing and basic. Accordingly, the corresponding neutral rhenium(II) and rhenium(III) hydride complexes are isolated following oxidation and protonation, respectively, of the anionic compound. Combination of the anionic rhenium(I) compound with ZnCl2 formed a tetrametallic Re(I)-Zn(I)-Zn(I)-Re(I) complex where the four metal centers are arranged in a nearly linear fashion. This compound is the first example of a Zn(I) compound to be supported exclusively by bonding to other metal centers. Computational and reactivity studies of this tetrametallic compound are also presented