Ruthenium complexes as molecular water oxidation catalysts

Aquesta tesi doctoral descriu la síntesi de complexos de ruteni i l'estudi de les seves propietats estructurals, espectroscòpiques, electroquímiques i catalítiques en l'oxidació d'aigua a oxigen. En particular, s’han desenvolupat un total d'onze compostos, que es poden dividir en dues grans famílies, amb: 1) Complexos amb lligand tetradentat equatorial dianionic, que coordina a través de dos grups piridina i dos carboxilats. S'han estudiat efectes de la segona esfera de coordinació i el mecanisme de la reacció. 2) Complex amb lligand tetradentat equatorial neutre, de tipus bis(fenantrolina) i els seus derivats. Aquest complex es transforma a un compost de tipus Ru-aquo que és actiu per a l'oxidació d'aigua a oxigen. Aquest últim es desactiva degut a la dimerització que forma un complex dinuclear amb un pont oxo (Ru-O-Ru). Aquest tesi evidencia la complexitat de la química de ruteni i les seves implicacions en la reacción d’oxidació d’aigua.Esta tesis doctoral describe la síntesis de complejos de rutenio y el estudio de sus propiedades estructurales, espectroscópicas, electroquímicas y catalíticas en la oxidación de agua. En particular, se han desarrollado once nuevos compuestos que se pueden clasificar en dos grandes familias: 1) Complejos con un ligando ecuatorial tetradentado dianiónico, que coordina a través de dos grupos piridina y dos carboxilatos. Se han estudiado efectos de segunda esfera de coordinación y el mecanismo de reacción. 2) Complejo con un ligando ecuatorial tetradentado neutro, de tipo bis(fenantrolina) y sus derivados. Este complejo se transforma en un compuesto de tipo Ru-aquo que es activo para la oxidación de agua a oxígeno. Éste último se desactiva debido a su dimerización para formar un complejo dinuclear con un puento oxo (Ru-O-Ru). Esta tesis pone de relieve la complejidad de la química de rutenio y sus implicaciones en la reacción de oxidación del agua.This thesis focuses on the synthesis of ruthenium complexes and the study of their structural, spectroscopic and electrochemical properties as well as their capacity to catalyse the oxidation of water to dioxygen reaction. In particular, eleven new compounds have been prepared that are included in two main families of complexes. 1) complexes containing a key equatorial tetradentate dianionic ligand that coordinates through two pyridinic groups and two carboxylate groups providing high electronic density to the metallic centre. Second coordination sphere effects and reaction mechanism have been thoroughly explored. 2) ruthenium complex containing an equatorial neutral ligand of the bis(phenantroline) family and their derivates. This complex converts to a Ru-aquo complex that is active for the water oxidation reaction. The latter evolves to an inactive dimeric complex that contains an oxo bridge (Ru-O-Ru). This thesis highlights the complexity of ruthenium chemistry and its implications in the water oxidation reaction

Characterization of Rigid Polyurethane Foam Prepared from Recycling of PET Waste

Poly (ethylene terephthalate) (PET) waste bottles were recycled to prepare RPUFs (rigid polyurethane foams) by using propylene glycol (PG) in different glycol/polymer molar ratios. The glycolysis products were characterized, after that, they reacted with poly methylene diphenyl diisocyanate (PMDI) in the presence of blowing, co-blowing and second blowing agents to produce the RPUFs. The prepared foams were characterized and compared to foam that is produced by original polyol. It was found that the glycolysis products have possibility for the fabrication of RPUFs with proper properties depending on the blowing agent type and density, also they have similar thermal stability compared to that one produced by original polyol. This may provide an advantage in the future planning for recycling of PET bottles to enhance the mechanical and thermal properties of PU

A Ru-bda complex with a dangling carboxylate group: synthesis and electrochemical properties

Ruthenium complexes containing the tetradentate 2,2'-bipyridine-6,6'-dicarboxylato (bda2-) equatorial ligand and ortho-subsituted pyridines in the axial position have been prepared and characterized using spectroscopic, crystallographic and electrochemical techniques. Complexes [Ru(Hbda)(DMSO)(pyC)] (1) and [Ru(bda)(DMSO)(pyA)] (2) (where pyC is 2-pyridinecarboxylate, pyA is pyridine-2-ylmethanol and DMSO is dimethylsulfoxide) have been isolated in moderate to high yields. The solid state structures of (1-H)- and 2 reveal the strong chelate effect of the axial pyridine ligand that coordinates in a bidentate fashion leaving the bda2- equatorial ligand coordinating in a tridentate mode. In solution, compound 2 shows a dynamic equilibrium between different coordination modes of the bda2- and pyA ligands. This phenomenon does not occur for 1 because the carboxylate binds stronger than the labile alcohol in 2. Cyclic voltammetry analysis of 1 reveal a complex behavior with a pH independent wave at E1/2 = 1.12 V that is tentatively associated with the two- electron RuIV/II. In sharp contrast, complex 2 shows a pH dependent one-electron wave at E1/2 = 0.83 V (pH 1), assigned to the proton couple electron transfer process of the RuIII/II couple and a pH independent wave at E1/2 = 1.06 V assigned to the RuIV/III couple. Compound 2 was used to prepare complex [Ru(bda)(pic)(pyA)] (4). This complex is air sensitive and converts to complex [Ru(bda)(pic)(pyE)] (5) (where pyE is methyl 2-pyridine carboxylate) in the presence of methanol. This oxidation also occurs by applying a positive potential to an aqueous solution of 4, producing the derivative [Ru(bda)(pic)(pyC)] (3). Cyclic voltammetry of 3 shows two pH independent one-electron oxidation waves at E1/2 = 0.64 V and E1/2 = 1.0 V, corresponding to the RuIII/II and RuIV/III couples, respectively. In addition, a water oxidation catalytic wave appears at Eonset ≈ 1.4 V. Foot of the wave analysis of this catalytic wave based on a water nucleophilic attack accounts for a TOFmax = 0.63-0.74 s-1

Characterization of Rigid Polyurethane Foam Prepared from Recycling of PET Waste

Poly (ethylene terephthalate) (PET) waste bottles were recycled to prepare RPUFs (rigid polyurethane foams) by using propylene glycol (PG) in different glycol/polymer molar ratios. The glycolysis products were characterized, after that, they reacted with poly methylene diphenyl diisocyanate (PMDI) in the presence of blowing, co-blowing and second blowing agents to produce the RPUFs. The prepared foams were characterized and compared to foam that is produced by original polyol. It was found that the glycolysis products have possibility for the fabrication of RPUFs with proper properties depending on the blowing agent type and density, also they have similar thermal stability compared to that one produced by original polyol. This may provide an advantage in the future planning for recycling of PET bottles to enhance the mechanical and thermal properties of PU

A broad view at the complexity involved in water oxidation catalysis based on Ru-bpn complexes

A new Ru complex with the formula [Ru(bpn)(pic)2]Cl2 (where bpn is 2,2′-bi(1,10-phenanthroline) and pic stands for 4-picoline) (1Cl2) is synthesized to investigate the true nature of active species involved in the electrochemical and chemical water oxidation mediated by a class of N4 tetradentate equatorial ligands. Comprehensive electrochemical (by using cyclic voltammetry, differential pulse voltammetry, and controlled potential electrolysis), structural (X-ray diffraction analysis), spectroscopic (UV-vis, NMR, and resonance Raman), and kinetic studies are performed. 12+ undergoes a substitution reaction when it is chemically (by using NaIO4) or electrochemically oxidized to RuIII, in which picoline is replaced by an hydroxido ligand to produce [Ru(bpn)(pic)(OH)]2+ (22+). The former complex is in equilibrium with an oxo-bridged species {[Ru(bpn)(pic)]2(μ-O)}4+ (34+) which is the major form of the complex in the RuIII oxidation state. The dimer formation is the rate determining step of the overall oxidation process (kdimer = 1.35 M−1 s−1), which is in line with the electrochemical data at pH = 7 (kdimer = 1.4 M−1 s−1). 34+ can be reduced to [Ru(bpn)(pic)(OH2)]2+ (42+), showing a sort of square mechanism. All species generated in situ at pH 7 have been thoroughly characterized by NMR, mass spectrometry, UV-Vis and electrochemical techniques. 12+ and 42+ are also characterized by single crystal X-ray diffraction analysis. Chemical oxidation of 12+ triggered by CeIV shows its capability to oxidize water to dioxygen

The Behavior of the Ru-bda Water Oxidation Catalysts at Low Oxidation States

The Ru complex [RuII(bda‐κ‐N2O2)(N‐NH2)2] (1; bda2−=2,2′‐bipyridine‐6,6′‐dicarboxylate, N‐NH2=4‐(pyridin‐4‐yl)aniline) was used as a synthetic intermediate to prepare new RuII and RuIII bda complexes that contain NO+, MeCN, or H2O ligands. In acidic solution complex 1 reacts with an excess of NO+ (generated in situ from sodium nitrite) to form a new Ru complex in which the aryl amine ligand N−NH2 is transformed into a diazonium salt [N‐N2+=4‐(pyridin‐4‐yl)benzenediazonium)] together with the formation of a new Ru(NO) moiety in the equatorial zone, to generate [RuII(bda‐κ‐N2O)(NO)(N‐N2)2]3+ (23+). Here the bda2− ligand binds in a κ‐N2O tridentate manner with a dangling carboxylate group. Similarly, complex 1 can also react with a coordinating solvent, such as MeCN, at room temperature to give [RuII(bda‐κ‐N2O)(MeCN)(N‐NH2)2] (3). In acidic aqueous solutions, a related reaction occurs in which solvent water coordinates to the Ru center to form {[RuII{bda‐κ‐(NO)3}(H2O)(N‐NH3)2](H2O)n}2+ (42+) and is strongly hydrogen‐bonded with additional water molecules in the second coordination sphere. Furthermore, under acidic conditions the aniline ligands are also protonated to form the corresponding anilinium cationic ligands N‐NH3+. Additionally, the one‐electron oxidized complex {[RuIII{bda‐κ‐(NO)3.5}(H2O)(N‐NH3)2](H2O)n}3+ (53+) was characterized, in which the fractional value in the κ notation indicates the presence of an additional contact to the pseudo‐octahedral geomet