Katrín Lilja Sigurðardóttir presents her research for Masters degree in Chemistry,
Abstract:
The project describes the breakdown process of monohalogenated silacyclohexanes (CH2)5SiHX; X = F, Cl, Br, I. Energy diagrams for the most common breakdown pathways were calculated by computational methods and they are compared to experimental breakdown diagrams, obtained by Threshold Photoelectron Photoion Coincidence (TPEPICO) analysis.
Breakdown analysis show that all of the four derivatives, except the I-substituted silacyclohexane dissociate in a similar manner. The F-, Cl-, and Br-substituted derivatives commonly dissociate by losing an ethylene fragment at the lowest energy onset but a propene loss is also observed to some degree. On the other hand, the first dissociation step of the I-substituted silacyclohexane is the loss of the halogen atom, resulting in a somewhat different breakdown pathway. Calculated breakdown diagrams reveal that the cleavage of ethylene and propene requires very different molecular rearrangement in order to pass through the transition state of the cleavages. Ethylene or propene loss requires similar energy for all the rings while the Si-X bond energy decreases considerably when going from the lightest halogen derivative to the heaviest, the Si-X bond cleavage being the lowest energy initial dissociation step for the I-substituted ring. Generally, this is in good agreement with the experimental breakdown diagrams.
The second part of the project describes the attempts to synthesize hitherto unknown compounds of ansa complexes. The main compounds are [5]Ferrocenophane and the analogous [5]Chromoarenophane, with the bridging 1,5-disilapentane ligands containing the reactive SiH2 groups.
Multiple attempts were made to synthesize the Fe-containing complex. NMR spectra of the products show a mixture of the desired complex and some side products but attempts to isolate and crystallize the complexes were not successful.
Advisors:
Professor Ingvar H. Árnason
Professor Ágúst Kvaran
External Examiner:
Pálmar Ingi Guðnason