Clústeres Sulfuro Trimetálicos de Molibdeno y Wolframio Funcionalizados con Ligandos Difosfina o Aminofosfina y sus Aplicaciones en Catálisis Orgánica

Abstract

<p> The research work described in this thesis presents the synthesis, characterization and properties of a new family of trimetallic M₃(&mu;₃-S)(&mu;₂-S)₃molybdenum and tungsten sulfide clusters. Functionalization of the cluster unit has been done by incorporating different chelating ligands such as diphosphines and heterodentate aminophosphines in order to confer specific physicochemical properties such as water solubility or catalytic activity. In particular, water&nbsp;soluble&nbsp;diphosphines&nbsp;and&nbsp;aminophosphines&nbsp;have&nbsp;been&nbsp;coordinated&nbsp;to&nbsp;the&nbsp;M₃S₄ unit in order to evaluate the potential applications of these new derivatives in environmentally friendly biphasic catalysis and homogenous organic catalysis, respectively.</p> <p> The first chapter of the thesis describes the background, relevance and importance of the chemistry of transition metal clusters. General aspects on the chemistry of molybdenum and tungsten trinuclear clusters are shown together with their last novel applications. The second chapter shows the main objectives of this research project.</p> <p> The preparation and characterization of novel water soluble cluster compounds of formula [M₃S₄X₃(hydroxyalkyldiphosphine)₃]⁺ (M=Mo, W; X=Cl, Br; hydroxyalkyldiphosphine = dhprpe, dhbupe) is described in chapter 3. Detailed studies based on ³¹P{¹H} NMR and electrospray ionization mass spectrometry techniques have been carried out in order to understand the complex pH dependent aqueous speciation of these water soluble clusters.</p> <p> In chapter 4, the synthesis of molybdenum (IV) hydroxo [Mo₃S₄(dmpe)₃(OH)₃]⁺&nbsp; and hydrosulfido [Mo₃S₄(dmpe)₃(SH)₃]⁺ trimetallic cuboidal cluster complexes is presented. A comparative study between molybdenum and tungsten of the gas-phase aldehyde production from the M₃S₄ ethoxo complexes combining collision induced dissociation experiments with computational DFT calculations is also discussed.</p> <p> In chapter 5, the catalytic activity of molybdenum and tungsten (IV) cluster hydrides of formula [M₃S₄H₃(dmpe)₃]⁺ (M=Mo, W) in the regioselective hydrodefluorination of pentafluoropyridine at the 4-position has been evaluated. A mechanism for the catalytic reaction has been proposed based on experimental results and DFT calculations. Additionally, the fluorinated [M₃S₄F₃(dmpe)₃]⁺ complexes have been fully characterized.</p> <p> In chapter 6, an aminophosphine ligand, (2-aminoethyl)diphenylphosphine (edpp),&nbsp; containing a NH₂ protonic function has been coordinated to the molybdenum and tungsten M₃(&mu;₃-S)(&mu;-S)₃ cluster unit to afford for the first time trimetallic aminophosphine complexes. The activity of the molybdenum [Mo₃S₄X₃(edpp)₃]⁺ (X=Cl, Br) clusters in the catalytic transfer hydrogenation of nitroarenes has been investigated. Cluster catalysis is demonstrated from reaction monitoring using a pressurized sample infusion (PSI) ESI mass spectrometric technique. The reactivity of the tungsten [W₃S₄Br₃(edpp)₃]⁺ cation&nbsp; towards alcohols, bases and halides salts has been investigated using a combination of spectrometric and spectroscopic techniques.&nbsp; Molybdenum and tungsten [M₃S₄X₃(edpp)₃]⁺ (X=Cl, Br) complexes have been derivatized to afford a novel family of&nbsp; trinuclear clusters bearing alkoxo terminal ligands.</p> <p> In Chapter 7, details of the synthetic procedures together with the experimental and theoretical characterization are shown. Finally, chapter 8 shows the main conclusions of this Ph. D. thesis.</p>