Metal compounds with rigid polyaromatic ligands. Catalytic consequences

En esta Tesis Doctoral se han preparado una serie de ligandos carbeno N-heterocíclico (NHC, por sus siglas en inglés) funcionalizados con sistemas poliaromáticos. En primer lugar se prepararon una serie de ligandos NHC que incorporan fragmentos poliaromáticos basados en pireno, fenantrofenacina y acenaftoquinoxalina. Estos ligandos fueron coordinados a fragmentos metálicos de iridio, rodio, níquel y paladio. Con fines comparativos, se obtuvieron los complejos análogos derivados de los ligandos imidazolilideno y benzoimidazolilideno. Los complejos derivados de iridio y níquel nos permitieron estudiar las propiedades electrónicas de los ligandos. De manera particular, en esta Tesis Doctoral se demostró, mediante cálculos computacionales de DFT, estudios de infrarrojo y electroquímicos, que las propiedades electrónicas de los ligandos poliaromáticos pueden ser moduladas mediante compuestos orgánicos que favorecen el apilamiento-¿ como, por ejemplo, pireno y hexafluorobenceno. Además, mediante técnicas experimentales y teóricas, se determinó de manera inequívoca la constate de asociación y la regioselectividad de la interacción entre los ligandos NHC con sistemas poliaromáticos y reactivos capaces de establecer interacciones de apilamiento-¿. Asimismo, se demostró que la actividad catalítica de algunos de los complejos preparados puede verse afectada por la presencia de un compuesto que favorezca el apilamiento. En segundo lugar, preparamos una serie de complejos di-metálicos y tri-metálicos basados en ligandos NHC, en los que las unidades carbeno se encuentran unidas por sistemas poliaromáticos extendidos. Cabe destacar que en la literatura hay muy pocos ejemplos de este tipo de complejos. Finalmente, se amplió la versatilidad coordinativa de los ligandos bis(NHC) derivados de bis(imidazolilidinas). Para ello hemos utilizado dos estrategias sintéticas: i) la doble activación C-H de un grupo C(sp3)H2 y ii) la activación de la sal de azolio con una base débil.Programa de Doctorat en Cièncie

A nano-sized Janus di-N-heterocyclic carbene ligand based on a quinoxalinophenanthrophenazine core, and its coordina- tion to iridium

A Janus-type bis-N-heterocyclic carbene ligand based on a quinoxalinophenanthrophenazine core has been obtained and coordinated to iridium. The electronic properties of the ligand have been determined on the basis of an evaluation of the Tolman electronic parameter values. The new ligand disposes the two metals at a distance of 22.4 Å, significantly longer than in any of the related ligands reported so far.CTQ2011-24055/BQU; MINECO; Ministerio de Economía y Competitivida

A Tetracyclic Bis(imidazolindiylidene) Ligand and Its Diiridium and Dipalladium Complexes

A bis(imidazolidine) with two butylene linkers between the nitrogen atoms of the adjacent heterocycles has been prepared. This tetracyclic molecule can be coordinated to iridium and palladium following two different methodologies. The coordination to iridium is achieved by double C(sp3)–H activation of the neutral tetracyclic bis(imidazolidine), which reacts with [IrCl(COD)]2 to afford the corresponding bis-NHC complex that contains two IrCl(COD) fragments. The reaction is facilitated by the addition of 1,5-cyclooctadiene, which is released from the reaction as cyclooctene. The reaction of the bis-NHC[IrCl(COD)] (bis-NHC = bis(imidazolindiylidene)) complex with CO allows the formation of the corresponding tetracarbonyl complex of diiridium. The molecular structures of the two iridium complexes have been determined by means of X-ray crystallography. The reaction of the tetracyclic bis(imidazolidine) with N-bromosuccinimide allows the formation of a tetracyclic bis(imidazolinium) salt, which serves as a traditional bis-NHC precursor. The reaction of this bis(imidazolinium) salt with Pd(OAc)2 in the presence of KI and in acetonitrile allows the formation of the bis-NHC[PdI2(CH3CN)]2 complex. The acetonitrile ligand can be easily replaced by reaction with 3-chloropyridine, affording the corresponding bis-NHC[PdI2(3-Clpyr)]2 complex. The two palladium complexes were tested in the acylation of aryl halides with hydrocinnamaldehyde, showing moderate to low activity

A pyrene-based N‑heterocyclic carbene: study of its coordination chemistry and stereoelectronic properties

A new pyrene-N-heterocyclic carbene ligand has been obtained and coordinated to rhodium and iridium, affording the corresponding [MCl(NHC)(COD)] and [MCl(NHC)(CO)2] complexes (M = Ir, Rh). The presence of the pyrene backbone allows the introduction of a η6 -bonded [RuCp]+ fragment and facilitates the formation of the corresponding heterometallic complexes of Rh/Ru and Ir/Ru. The stereoelectronic properties of the new ligand have been studied by means of IR spectroscopy and cyclic voltammetry and demonstrate that the introduction of the [RuCp]+ fragment results in the reduction of the electron-donating power of the ligan

Experimental and Theoretical Approaches to the Influence of the Addition of Pyrene to a Series of Pd and Ni NHC-Based Complexes: Catalytic Consequences

A series of Ni and Pd complexes with three different N-heterocyclic carbene (NHC)-based ligands (imidazolylidene, benzimidazolylidene and pyrene–imidazolylidene) has been prepared and fully characterized. The influence of the addition of pyrene to solutions containing these complexes is studied by means of NMR and UV/Vis spectroscopies and by cyclic voltammetry. The addition of pyrene to the pyrene–NHC-containing Pd and Ni complexes gives rise to the formation of adducts by π–π stacking interactions between pyrene and the pyrene group of the NHC ligand. This interaction causes a modification of the electronic properties of the metal, as demonstrated by cyclic voltammetric studies of the Ni–NHC complexes. Theoretical calculations support this type of π-interactions, and justify the higher interactions observed with the pyrene–NHC containing complexes. The catalytic activities of the complexes were tested in the Suzuki–Miyaura C[BOND]C coupling and in the α-arylation of ketones. The addition of pyrene as an external π-stacking additive does not affect the activities of the complexes in the Suzuki–Miyaura coupling, but this observation may be justified due to the fact that the process is heterogeneously catalyzed, as indicated by the mercury-drop test. The addition of pyrene to the catalytic α-arylation of ketones results in a decrease in the activity of the reactions catalyzed by the pyrene–imidazolylidene palladium complex, whereas the other two catalysts do not modify their activity in the presence of this π-stacking additive.MEC of Spain (CTQ2011-24055/BQU and CTQ2011-23336) and UJI(P1.1B2011-22