Reactivity of the gas phase and in solution of group 9 metal olefin complexes
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Number of pages
VIII, 194 p.
RU,, 06 juli 2005
Promotores : Nolte, R.J.M., Plattner, D., Chen, P. Co-promotor : Bruin, B. de
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SubjectPhysical Organic Chemistry
The reactivity of rhodium(I) and iridium(I) ethene complexes with tri- and tetradentate nitrogen donor ligands towards dioxygen has been investigated both in the gas phase, in solution and in the solid state. Since the reactivity of organometallic complexes can be very complex in all phases, a comparison of the reactivities in each phase can be very useful and provide more insight into certain steps in a reaction mechanism. Such comparisons may also give information about the reasons for observed low complex stabilities. The influence of the steric bulk on the reactivity was investigated as well. In solution only for the sterically hindered complexes products could be isolated: peroxo and peroxo-ethene complexes. No C-O bond formation took place. In the solid state no selective reaction could be observed. In all cases where more than one product was obtained paramagnetic species were among the products formed. From reaction of iridium(II) ethene complexes with dioxygen it became clear that unlike iridium(I) species, the iridium(II) complexes are capable of C-O bond formation. Such insight is of importance for the development of catalytic olefin oxygenation by group VIII metal centres. Gas-phase behavior of the rhodium(I) and iridium(I) ethene complexes correlates well with stabilities in solution. Upon collision with dioxygen in the gas phase only diamagnetic products are formed: peroxo complexes for rhodium and peroxo-ethene complexes for iridium. The type of complexes that are reactive in the gas phase and the mechanism via which they react (associative or dissociative) depends on the region of the mass spectrometer. Contrary to solution no electron transfer reactions take place in the gas phase. In those cases where electron-transfer processes compete with formation of peroxo or peroxo-ethene species, the paramagnetic pathway is shut off in favour of the diamagnetic pathway.
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