Organometallic chemistry of some manganese and zirconium complexes: A green chemistry approach

Stanley, Manzini
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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 iii iv 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.
Faculty of Science School of Chemistry 9309501t
Organometallic, Chemistry, Green, Solventless, Synthesis