AbstractsChemistry

This dissertation investigates three topics in the field of multiple-bonded metal chemistry. The first topic concerns the synthetic and theoretical considerations of ditungsten formamidinates and guanidinates compounds. This work presents an enhanced synthetic path to the W2(hpp)4 molecule (Hhpp = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine). The reflux of W(CO)6 with Hhpp in o-dichlorobenzene at 200 oC produces W2(hpp)4Cl2 in a one-pot reaction in 92% yield. This compound is stable and easily stored for further use, and it can be efficiently reduced in a one-step reaction to the most easily ionized compound W2(hpp)4. This work also examines the electronic structure and geometry of the intermediates W2(????-CO)2(????- hpp)2(????2-hpp)2 and W2(hpp)4Cl2. The second topic concerns the theoretical investigation by DFT of the electronic structure of [Mo2] units bridged by oxamidate ligands or bridging hydride ions ([Mo2] = (Mo2(DArF)3, where DArF is the anion of a diarylformamidine). It is shown that the effect of the gauche conformation of the ???? oxamidate isomers is due to steric interactions, and that the planar ???? oxamidate isomers have an electronic structure similar to that of naphthalene when it is doubly oxidized. The [Mo2](????-H)2[Mo2] compound shows interdimetal unit interactions between the ???? orbitals of the two [Mo2] units. These interactions are theoretically predicted and experimentally observed by a decrease in the [Mo2] – [Mo2] distance with a one-electron oxidation of [Mo2](????- H)2[Mo2]. The final topic concerns the magnetic and structural properties of two Ru2(DArF)4Cl compounds. The compounds with Ar = p-anisyl (para) and m-anisyl (meta) both show different temperature dependence of their molar magnetic susceptibility, ????. For the para compound, there is a Boltzmann distribution between a ????*3 ground state and a ????*2????* upper state, and this is confirmed by a temperature dependence of the Ru-Ru bond length: 2.4471(5) ???? at 23 K and 2.3968(5) ???? at 300 K. For the meta compound, a ????*2????*configuration persists over the range of 23-300 K as shown by an invariant Ru-Ru bond length and its molar magnetic susceptibility.