Reactions of some cobalt and rhodium complexes of macrocyclic N-donor ligands

Joshua, Warren A. C. (1991) Reactions of some cobalt and rhodium complexes of macrocyclic N-donor ligands. (PhD thesis), Kingston Polytechnic, .


This thesis is principally concerned with the interaction of cobalt porphyrin complexes with halocarbons. There have been no previous studies of these, despite the afct that the ability to readily introduce substituents into the porphyrin ligand makes it ideal for inducing subtle electronic and steric changes into the complexes. The reactions of various substituted cobalt tetraphenylporphyrins with halocazbons was studied. Three series of experiments were performed involving activation by heat, visible light and ultraviolet light. Products were characterized by electronic, nmr and mass spectrometry. The five coordinate complexes, [CoX (Por)] , obtained from thermally activated reactions and those performed with uv irradiation under nitrogen, proved particularly difficult to characterize since they are subject to disproportionation giving paramagnetic products. This aspect is discussed in detail and the results obtained allow clarification of conflicting reports in the literature. A qualitative investigation of relative reaction rates has led to the tentative suggestion that thermal reactions proceed by an electron transfer mechanism, whereas an atom abstraction mechanism applies to reactions involving activation by ultraviolet light. No reaction took place between cobalt porphyrins and the substrates in the presence of visible light. Aerobic ultraviolet radiation results in the formation of cobalt porphyrin [pi]-cation radicals with either a1u or azU. ground states, depending on the substituent pattern of the porphyrin. The cobalt porphyrins were all shown to possess catalytic activity for halocarbon-alkene addition reactions. Furthermore, studies in this area suggest that the catalytic activity could be correlated wíth the substituent pattern on the porphyrin ligand and, thus, complements the studies described above. A related rhodium complex was also synthesized and examined but was shown to have a disappointingly low catalytic activity. Products of [RuC1[sub]2z(PPh[sub]3)[sub]3] -catalysed additions of halocarbons to cyclohexa-1,3-diene were investigated by chromatographic and spectroscopic analyses to ascertain the stereochemistry of the products. The ratio of the two isomeric products was found to depend on steric effects of the addend groups, CX[sub]3 (X = Cl, Br) and X (X = Cl, Br).

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