Complejos metal-carbeno de Fischer nitrogenadosMecanismos fotoquímicos y propiedades fotofísicas stars

  1. Susana López Sola
Supervised by:
  1. Pedro José Campos García Director
  2. Miguel Angel Rodríguez Barranco Director

Defence university: Universidad de La Rioja

Year of defence: 2007

Committee:
  1. Gregorio Asensio Aguilar Chair
  2. Diego Sampedro Ruiz Secretary
  3. Kilian Muñiz Committee member
  4. María Consuelo Jiménez Molero Committee member
  5. Alfredo Ballesteros Gimeno Committee member
Doctoral thesis with
  1. Mención internacional
Department:
  1. Chemistry

Type: Thesis

Abstract

This work is centered on the behavior of Fischer imine carbene complexes towards light. The following objectives of study were planned: the stereoselectivity in reactions with alkenes to form 1-pyrrolines, the influence of substituents in the photoreactivity and the phophysical properties of imine carbene complexes. Chromium complexes are employed in the study of reactivity and chromium and tungsten complexes in the analysis of photophysical properties. In Chapter 3, the synthesis, X-Ray structures and irradiations of alkoxy- and imine carbene complexes are described. The stereoselectivity of the formation of 1-pyrrolines from the irradiation of Fischer imine carbene complexes and alkenes is studied through the introduction of chiral auxiliars. The reaction proceeds through intermediate N-cyclopropylimines that suffer photochemical rearrangement. Moreover, they can racemize and isomerize photochemically limiting the stereoselectivity of the global process. Certain grade of diastereoselectivity can be achieved when the chiral auxiliar is conserved along the process. Next, modifications of substituents in the irradiations of imine carbenes with alkenes and alkynes are carried out. On the one hand, the photolysis of the ethoxy imine carbene 10, which leads to five member heterocycles without CO insertion, indicates that the imine group determines the reactivity and inhibits the insertion. On the other hand, several irradiations in the presence of alkynes support the mechanistic proposal for the three types of products formed in the reactions: 2H-pyrroles, indenes and azadendralenes. Furthermore, irradiations of imine carbene complexes with other unsaturated compounds are carried out. In addition, the synthesis of a new carbene complex by nitrogen radical addition to an alkynyl methoxycarbene is reported. The radical is generated by photolysis of the O-acyloxime benzophenone. Chapter 4 deals with the photophysics of the complexes. The shapes of the theoretical absorption spectra (TD-DFT) of alkoxycarbene 4 and iminecarbene 11 are compared with the UV-vis spectra bands. The luminescence of several Cr and W alkoxy and imine carbene complexes is measured. Finally, triplet excited specie generated from the imine carbene 11 is detected, both by direct detection and by quenching of the xanthone triplet.