Faculty of Science
School of Chemistry
9309501t
Stanley.manzini@up.ac.za / The solventless reaction between Mn(CO)4(PPh3)Br and PPh3 as neat reagents using
FTIRS was conducted and the activation enthalpy change of formation was found to be
143 ± 19 kJmol-1 while the activation entropy change of formation was 104 ± 7 Jmol-1K-1.
The same reaction was also carried out in chloroform and the activation enthalpy change
of formation was found to be 146 ± 8 kJmol-1 while the activation entropy change of
formation was 114 ± 6 Jmol-1K-1. When the reaction was conducted in TCE solution, the
activation enthalpy and entropy changes of formation were 137 ± 6 kJmol-1 and 97 ± 5
Jmol-1K-1 respectively.
The solventless reaction of Mn(CO)4(PPh3)Br with PPh3 in KBr matrix using DRIFTS
was also conducted and the activation enthalpy change of formation was found to be 169
± 28 kJ.mol-1 while the activation entropy change of formation was 204 ± 57 J.mol-1.K-1.
The sample preparation method, the type of support and the particle size of the support
material influenced the reaction rate. The soventless reaction Mn(CO)4LBr + L →
Mn(CO)3L2Br + CO [L= P(p-C6H4-R)3, R = Ph, MeO, Cl, F] in KBr using DRIFTS was
also studied. It was found that the electronic effects of the ligand already attached on the
metal complex influenced the rate of the reaction.
An optical microscopy study of the reaction Mn(CO)4LBr + L' → Mn(CO)3LL'Br + CO
[L= P(p-C6H4-R)3, R = H, Ph, MeO] was undertaken in an attempt to reconcile the wellbehaved
reaction kinetics of the solventless reactions with solventless reactions by
observing the microscopic behaviour of the reagents. The reactions were observed to go
through a melt phase at temperatures much lower than the lowest melting point of the
reagents, provided the reagents were in contact with each other. Isolated reagents neither
reacted nor melted. The molten reagent thus served as a medium that allowed the
diffusion of the reagents and products to ensure well-behaved kinetics. Investigation
using 31P NMR demonstrated that the dissociation of the attached phosphine ligands also
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took place. The evidence obtained using the various techniques enabled the elucidation of
the reaction mechanism.
The solventless reaction, (η5-C5H5)2ZrCl2 + Na+RCOO-, R = C6H5, p-C6H4-NO2, p-C6H4-
NH2 → (η5-C5H5)2ZrCl(RCOO) + NaCl did not occur but the reaction was found to take
place in the NMR solvent. Single crystal XRD study of (η5-C5H5)2ZrCl(RCOO) R =
C6H5, p-C6H4-NO2 revealed that the carboxylato ligand was coordinated in a bidentate
fashion.
The reaction of chlorobis(η5-cyclopentadienyl)hexylzirconium(IV) with internal hexene
isomers failed to yield terminal olefins even under harsh experimental conditions.
Isomerisation reactions using substituted zirconium metallocenes also failed to produce
the terminal olefin. The reaction of Cp2ZrCl2 / n-BuLi with internal hexenes yielded a
stoichiometric amount of 1-hexene. The reaction was found to be catalytic in Cp2ZrCl2
but limited by the amount of n-BuLi.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/1482 |
| Date | 27 October 2006 |
| Creators | Stanley, Manzini |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 10226466 bytes, application/pdf, application/pdf |
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