The principal goal of this work was to synthesize and fully characterize a range of free / Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2007.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

This work is aimed at elucidating the structures and spectroscopic properties of phosphine and b phosphonite complexes of Mn(III), Co(III) and Rh(III) porphyrins, a class of coordination compounds that has been little reported on in the literature to date. In this work, a range of novel bis(phosphine) and bis(phosphonite) complexes of the three aforementioned metals have been synthesized, crystalized and analysed by means of X-ray structure determination, 1H NMR, 13C NMR, 31P NMR as well as electronic and IR spectroscopy. [Mn(TPP)(PPh3)2](SbF6) crystallizes in the monoclinic space group P21/c and displays an extraordinarily long Mn-P bond length of 3.088(2) A. Moderate ruffling of the porphyrin ligand is observed. This complex is paramagnetic with fast proton relaxation times, and thus did not yield any useful 1H NMR data. In an attempt to crystallize [Mn(TPP){P(OPh)3}2](SbF6), a complex bearing an O-donor contamination product, [Mn(TPP){(O)PH(OPh)2} ](SbF6), was isolated and its solid state structure determined by X-ray diffraction methods. The structure of this complex has been included in this work as it displays interesting structural features and is the very first phosphonate complex of a metalloporphyrin. This compound crystallizes in the monoclinic space group P21/n and shows a significantly saddled conformation. The axial Mn-O bond length measures 2.122(3) A. The Mn-Nporph bond lengths are 1.998(6) and 2.002(3) A for the bis(phosphine) and phosphonate complexes, respectively. Since the diethyl phosphonate complex was an unintended reaction product, no further characterisation of it was undertaken. [Co(TPP)(depp)2](SbF6), where depp = diethylphenylphosphine, crystallizes in the monoclinic space group P21/c. This complex displays inversion symmetry at the metal center and the porphyrin core is effectively planar. However, [Co(TPP)(edpp)2](SbF6), where edpp = ethyldiphenylphosphine, crystallizes in the· monoclinic space group P21/n and shows a significantly ruffled conformation of the porphyrin core and displays no inversion symmetry. [Co(TPP)(deppt)2](SbF6), where deppt = diethylphenylphosphonite, also crystallizes in the monoclinic space group P21/n, but displays inversion symmetry through the central cobalt ion. As a result, this complex does not display any significant conformational deviations of the porphyrin core from planarity. The axial Co-P bond lengths are significantly shorter than that of . the equivalentbond in the manganese bis(triphenylphosphine) complex at 2.312(1) A, 2.323(10) A and 2.258(2) A for [Co(TPP)(depp)2](SbF6), [Co(TPP)(edpp)2](SbF6) and [Co(TPP)(deppt)2](SbF6), respectively. The Co-Nporph bond lengths average to 1.980(3) A, 1.972(7) A and 1.980(4) A for these three complexes, respectively. I03Rh NMR measurements of three rhodium bis(phosphine)/bis(phosphonite) porphyrins have been performed by the indirect probing of the rhodium metal center by means of the phosphorus nucleus of the coordinated axial ligand. The resulting I03Rh NMR shifts for [Rh(TPP)(edpp)2](SbF6), [Rh(TPP)(edppt)2](SbF6), where edppt = ethyldiphenylphosphonite, and [Rh(TPP)(deppt)2](SbF6) are 2558, 2413 and 2365 ppm, respectively. [Rh(TPP)(edpP)2](SbF6) crystallizes in the monoclinic space group P21/n and shows moderate ruffling of the porphyrin core. The axial Rh-P bond length is 2.401(2) A. [Rh(TPP)(edppt)2](SbF6) and [Rh(TPP)(deppt)2](SbF6) both crystallize in the monoclinic space group P21/c. The porphyrin core of [Rh(TPP)(edppt)2](SbF6) displays a moderate degree of ruffling, as observed in [Rh(TPP)(edpp)2](SbF6), yet the axial Rh-P bond length is substantially shorter at 2.361(9) A. [Rh(TPP)(deppt)2](SbF6) exhibits the shortest Rh-P bond length of the three complexes at 2.332(2) A. The porphyrin core is mostly planar. The Rh-Nporph distances average 2.034(1) A for the S4-ruffled complexes and 2.044(3) A for the planar complex, the shorter distance in the ruffled derivatives being consistent with a distortion-induced compression of the Rh(III) ion. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003

The work presented in this dissertation describes the prepartion and characterisation of various strapped porphyrin compounds which are designed to model cytochrome P450 and the charge separation in photosynthesis. The major part of this work is concerned with models of cytochrome P450. After a brief introduction to the philosophy of modelling, there follows a review of work on the enzyme and various compounds which are designed to reproduce the enzymic characteristics. The synthesis of two singly bridged porphyrins is reported. These incorporate a pendent methyl ester in the centre of the strap and aim to mimic the proposed acylation step in the catalytic cycle. Evaluation as models was performed by a series of experiments involving the addition of potassium superoxide to the manganese complexes of these compounds. Characterisation of the mode of reactivity required the use of many physical techniques and necessitated the synthesis of a radio-labelled sample of one of the porphyrins. The results obtained suggest that superoxide binds preferentially to the bridge-free face of the macrocycle. Doubly bridged analogues of the above models were prepared which force the two faces of the porphyrin to be equivalent. Superoxide binding studies indicated a different mode of reactivity to the singly bridged models, for one of the compounds, and experiments to distinguish between possible interpretations of the results are suggested. A crown ether thiolate doubly bridged porphyrin was prepared as a model for the carbon monoxide complex of the enzyme. This was characterised by ultraviolet spectroscopy and attempts to produce a stable crystalline adduct are described. The remaining part of this work concerns a model for the charge separation process in photosynthesis. A discussion of natural systems and previous models is followed by a description of a tetraene pyromellitimide doubly bridged porphyrin, which shows significant quenching of the porphyrin fluorescence.

No description available.

No description available.

The tolyporphin A structure contains a tetrapyrrolic bacteriochlorin macrocycle and also consists of two glycosyl groups directly connected to the pyrroles. In this thesis, 3-glycosylated pyrrole was reacted with Eschenmoser's salt to produce N,N-dimethylamino methylated derivative in 95 % yield. Then, the product was reacted with pyrrole under microwave irradiation to produce glycosylated dipyrromethane in 44 % yield. Mono-glycosylated porphyrin was formed by reacting glycosylated dipyrromethane with 1,9-bis (imino)-5-phenyl dipyrromethane under the standard procedure, 1H NMR was used to confirm the new products.

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).

acase@tulane.edu / 1 / hong zhang