| dc.description.abstract | With the rapid development of computing technologies and the continuous improvements in quantum mechanical methods, modern computational chemistry has emerged as an indispensable tool in predicting transition-metal mechanisms and understanding metal-metal interactions. After a brief introduction to the computational methodology in Chapter I, Chapters II, III, and IV focus on three projects related to the chemistry of transition metal systems.
The first project is concerned with unexpected product distribution in the C-H activation of the (η5-C5Me5)IrPPh3 complex, which is generated upon photolysis of (η5-C5Me5)IrPPh3(H)2 in benzene. This reaction, unlike classical photoinitiated C-H activation reaction that typically proceed in pure solvent as the only reactant, involves both intramolecular and intermolecular reactions. Despite large concentration differences in the two reactions, they produced the ortho-metalated product and the hydridophenyl product in a nearly equal ratio. Density functional theory (DFT) calculations suggest that stable π-intermediates were formed before the oxidative addition in both cases. From the calculations, rapid interchange of the two pathways is necessary to justify the experimentally observed product distribution.
In the second project, a variety of computational analysis techniques: natural bonding orbital (NBO), quantum theory of atoms in molecules (QTAIM), and energy decomposition analysis (EDA) were used to understand the nature of the bond between the lanthanide and transition metal in recently synthesized PyCp2Ln-TMCp(CO)2 (DyPyCp22- = [2,6-(CH2C5H3)2C5H3N]2-, TM = Fe, Ru) complexes. This work concludes that the Ln-Fe bonds are best described as dative bonds with strong electrostatic contributions as well as significant orbital mixing, and important dispersion contributions. This conclusion very likely holds for the entire lanthanide series.
The third project focuses on the structure and reactivity of a family of closely related bridged-dicyclopentadienyl diruthenium complexes. The mechanism calculated for the carbon-hydrogen bond activation and silylation of benzene by the catalyst cis-{(η5-C5H3)2(CMe2)2}Ru2(κ2-4,4-di-tert-butyl-2,2-bipyridine)2-(μ-H)]+ seems to involved steps with very high barriers. Lower energy routes are predicted for simpler fragments of the catalyst. For the related [cis-{(η5-C5H3)2(CMe2)2}Ru(CH3)(CO)2Ru(CO)2]+ complex, calculations predicted a low energy route for transfer of a methyl group from a terminal metal site to the cyclopentadienyl ligand and of a H in the other direction. Finally, the molecular orbital diagram of [cis-{(η5-C5H3)2(CMe2)2}Ru2(CO)4(μ-Η)2]2+ demonstrated that each bridging H was bound by a 3c-2e bond, and in fact there was no effective Ru-Ru bond in the tetracarbonyl bridging dihydride dication. | en |
