Identifier: TDX:860
Authors: Gracia Budria, José Manuel
Abstract:
The overall framework of this report aims to summarize the work we have done over the past four years. Conceptually, this thesis is divided into three parts. The nucleus is based on a joint project with prof. Mena, of the University of Alcalá, whose group is involved in the synthesis and characterization of new aza- and oxo- titanium cubanes. These families of compounds are basically obtained from preorganized titanium tridentate ligands which can incorporate almost all the metals of the periodic table and yield the corresponding heterometallic cubanes. In this respect, the theoretical study is based on and adapted from the progress in the laboratory work. Practically every section in this part starts by describing the experimental data available for the specific system studied when we began the analysis. Then we go on to describe the theoretical study and attempt to involve the reader in the problems discussed. As a consequence of the advance in the experimental work, NMR spectra are used to characterize the new compounds. This leads us to initiate studies in the computational simulation of NMR chemical shifts. The most theoretical part of this report is an assimilation of these studies. The excellent results obtained for the cubane compounds enabled us to extend the knowledge acquired to other interesting fields and our group has started a study of the NMR shielding tensors in polyoxometalate compounds. The third part of the thesis focuses on some molybdenum-sulphide clusters and their activity as catalysts.Chapters 3 and 4 focuse on the electronic structure of the new titanium cubane compounds recently synthesized by Mena et al. We work parallel to an experimental group to compare and contrast the theoretical and experimental data, and so establish the base chemistry of these new compounds. In this sense, the various reaction energies were studied, and the compounds and their possible isomers were characterised by means of DFT methods. Particular emphasis is paid to the properties of incomplete Ti3 core cubane tridentate ligands (precubanes) as bases for obtaining cubanes. The electronic structure, bonding energies, electron transfer processes and reactivity in the titanium Ti3 core of the metal clusters are studied.The reaction of the azatitanium compound with some titanium derivatives leads to nitrocubane formation (see Scheme 1.3). This reaction forms a cubane compound by adding the fourth vertex to a structure that becomes a precubane. Scheme 1.3. Reaction of with Chapter 5 summarizes the work carried out during a six-month stay in Dr. John E. McGrady's group, which uses density functional theory to explore problems of structure, bonding and reactivity in inorganic compounds. The main focus of the research is metal-metal bonding in cluster compounds. Transition metals have a prominent position in catalysis, both in industrial and biological contexts, and the ultimate goal is to understand the part played by the metal and its ligand environment in facilitating a particular chemical transformation. Chapter 5 studies the electronic structure of the core catalysts and the mechanism of their, unresolved, catalytic activity. The various possible isomers with the generic formula were studied, and the energy of the electron transfer between the metallic centres and the sulphide ligands, so important in the catalytic process, was investigated in depth. Subsequently, the mechanism of the hydrogen activation reaction promoted by these bi-molybdenum compounds (Equation 1.1) was studied, and the nature of the different reaction pathways was elucidated.[(CpMo(-S))2(S2CH2)] promotes the hydrogenation of alkynes to cis alkenes, allenes to alkenes, and ketenes to aldehydes and the hydrogenolysis of carbon disulphide to hydrogen sulphide and thioformaldehide. The mechanisms of hydrogen interaction with these complexes have not been established. It is apparent that the sulphide ligands play a role in hydrogen coordination, and this ligand reactivity was a dominant characteristic throughout the study of these dinuclear molybdenum systems. Equation 1.1
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