Current industrial processes for the production of polycarbonates, a thermoplastic valued for commercial applications, leave much to be desired from an environmental viewpoint. Research into alternative methods for production of polycarbonates has focused on the copolymerization of carbon dioxide and epoxides for the benefits of eliminating phosgene as a reagent, and for the economic impact of incorporating CO2 as a low cost C1 feedstock. Early work in this field focused on the use of zinc-derived catalysts, but recent studies indicate that chromium complexes of the salen (N,N-bis-(salicylidene)-1,2-ethylene diimine) family of ligands are far superior to the zinc complexes in terms of reactivity and diminishing the formation of unwanted byproducts. Concomitant to the studies of chromium salen complexes, investigations of main-group salen metal complexes were carried out. Aluminum complexes were able to produce polycarbonate in the presence of tetrabutyl ammonium salts and neutral Lewis bases. Gallium complexes were essentially inactive for generating any product. Tin(IV) complexes were active for the production of polyether, the result of homopolymerization of epoxide without CO2 insertion. Tin(II) complexes generated the monomeric cyclic carbonate product but no copolymer. An additional aspect of research relative to this field of study is the development of polymeric materials from several different epoxide monomers. The complex [hydrotris(3-phenyl-pyrazol-1-yl)borate]Cd(II) acetate was used to study the thermodynamics of the binding of a series of potential epoxide monomers to a metal center via 113Cd NMR. Activation of the epoxide by a metal center was found to not play a significant role in the ability of the complex to be subsequently ring-opened for polymerization. A final relevant area of study involved the synthesis of cadmium analogues of Fe/Zn double metal cyanide (DMC) complexes. Heterogeneous DMCs are well known in patent literature as excellent catalysts for the production of polycarbonates and cyclic carbonates from CO2 and epoxides. Previous studies on homogeneous Fe/Zn DMCs have only provided cyclic carbonate. Cd analogues of these species provide a convenient NMR handle for studies on the activity of the metal centers in presence of an epoxide and by changes to the DMC structure.

Made available in DSpace on 2015-05-14T13:21:28Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 3057605 bytes, checksum: 28d023a60720f2efcfba34ac8067319f (MD5) Previous issue date: 2013-07-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / We describe here the synthesis and characterization of six compounds derived from Meldrum's acid inspired in the classic salens/salofens systems: four ligands (H2melen, H2Cy2melen, H2melophen, and H2Cy2melophen) and two Mn complexes [MnII(melophen)·1,7H2O and MnII(Cy2melophen)·1,7H2O]. Only H2melofen has been previously described. The ligands were synthesized via the reaction between a 5-methoxymethylene derivative of Meldrum's acid and the diamines ethylenediamine or o-phenylenediamine, resulting in the ligands melens or melofens, respectively, in moderate-to-high yields. The melens and melophens were characterized by 1H and 13C NMR, IR, and ESI-MS. UV-vis studies and thermal analysis (TG/DTA) of this class of compounds were reported here for the first time. Molar absorptivity (ε) for the absorption maxima in EtOH and DMSO were determined. TG/DTA studies were consistent with a two-step process: decomposition of the Meldrum ring (with loss of CO2 and ketone) yields likely a bis-ketene, which is then fully oxidized at high temperatures. The synthesis of new Schiff-base-type coordination compounds ,using Mn(OAc)2·4H2O as a source of Mn led to the isolation of MnII(melofen)·1,7H2O and MnII(Cy2melofen)·1,7H2O in 45% and 47% yield, respectively; all attempts to metallate the melens compounds were unsuccessful. The Mn-melophens proved insoluble in water and of low stability to acidic demetallation. Data of ESI-MS, TG/DTA, conductimetry, FT-IR and UV-vis spectroscopies, cyclic voltammetry and elemental analysis (%Mn) were used to characterize the MnII-melophens and are consistent with the isolation of Mn(II) complexes, in contrast with the Mn(III) complexes of MnIII-salophens. The metallation stabilized Meldrum´s ring thermally, but, once decompose began with loss of CO2 and ketone, the presence of manganese facilitated the combustion of the remaining organic matter. The effect of increasing the Mn(III)/Mn(II) reduction potential for the design of SOD mimics and cytochrome P450 models based on this new class of ligands is discussed. / Descreve-se aqui a síntese e caracterização de seis compostos derivados de ácido de Meldrum inspirados nos clássicos salens/salofens, sendo quatro ligantes (H2melen, H2Cy2melen, H2melofen e H2Cy2melofen) e dois complexos de Mn (MnII(melofen)·1,7H2O e MnII(Cy2melofen)·1,7H2O). Apenas o composto H2melofen não é inédito. Os ligantes foram sintetizados através da reação entre os derivados 5-metoximetilênico do ácido de Meldrum e diaminas etilenodiamina ou o-fenilenodiamina, resultando nos ligantes melens ou melofens, respectivamente, com bons rendimentos, melens (77% e 83%) e melofens (71% e 46%). Os melens e melofens foram caracterizados por RMN de 1H e 13C, IV, e ESI-MS. Estudos de UV-vis e de análise térmica (TG/DTA) dessa classe de compostos foram reportados pela primeira vez. Absortividades molares (ε) dos máximos de absorção em EtOH e DMSO foram determinadas. Os estudos de TG/DTA são consistentes com um processo em duas etapas: a decomposição do anel de Meldrum (com liberação de cetona e CO2) resulta, possivelmente na formação de um bis-ceteno, que é, em seguida, oxidado em elevadas temperaturas. A síntese de novos compostos de coordenação do tipo base de Schiff, usando Mn(OAc)2·4H2O como fonte de Mn, resultou nos complexos MnII(melofen)·1,7H2O e MnII(Cy2melofen)·1,7H2O em rendimentos de 45% e 47%, respectivamente; todas as tentativas de metalação dos melens foram sem sucesso. Os Mn-melophens mostraram-se insolúveis em água e de baixa estabilidade frente à desmetalação ácida. Os dados de ESI-MS, TG/DTA, condutimetria, espectroscopia (UV-vis e IV), voltametria cíclica e análise elementar (%Mn), foram usados na caracterização dos MnII-melofens e são consistentes com o isolamento de complexos de Mn(II), em contraste com os de Mn(III) dos MnIII-salofens. A metalação estabilizou termicamente o anel de Meldrum, mas, uma vez iniciada a decomposição daquele com a perda de CO2 e cetona, a presença do Mn facilitou a combustão da matéria orgânica restante. O efeito do aumento do potencial de redução Mn(III)/Mn(II) para o design de mímicos de SOD e de citocromos P450 à base dessa nova classe de ligantes é discutido.

A series of new cobalt(II) beta-keto iminato complexes and cobalt(II) salens have been made and the effect of chirality in the northern, southern and peripheral quadrants of these catalysts, with respect to induced enantiomeric excess, during the ring-opening of 1,2-dioxines has been determined. Synthesis of a series of cobalt beta-keto iminato complexes was achieved after modification of literature procedures used for the synthesis of manganese beta-keto iminato complexes and this procedure was applied to generate ligands with ethyl, t-butyl, (-)-bornyl, (+)-menthyl and (-)-menthyl esters and a methyl side chain. Synthesis of the cobalt salens was also achieved using a modified literature procedure, in respect to the more complex aldehydes made. It was ascertained that chirality in the northern quadrant of these catalysts, obtained by the use of optically pure diamines, was of greatest importance in introducing enantiomeric excess into the products of ring-opening of 1,2-dioxines; namely gamma-hydroxy enones, and chirality in the southern and peripheral quadrants was of lesser, although still significant, importance. The reaction conditions were optimised and the conditions under which the highest enantiomeric excess was introduced were determined. The ideal solvent for the ring-opening was found to be THF with a catalyst concentration between 5 and 10 mol% at a temperature of -15oC. These conditions were found to be applicable to all catalysts and 1,2-dioxines tested. Enantiomeric excess as high as 76 % could be introduced when the optimised reaction conditions were used in large scale syntheses of cyclopropane (61). LC-MS studies indicate the presence of a solvent chelated species present in the reaction mixture when the solvent used is THF, however, the use of non-chelating solvents, such as dichloromethane, did not exhibit this same solvent chelated species. Catalyst dimers were also present in the mixture when analysed by LC-MS. The presence of oxygen in the reaction mixture was found to inhibit rearrangement of the dioxine with catalyst oxygen dimers (two molecules of catalyst bound to a single molecule of oxygen) present when analysed by LC-MS, however, the catalyst could be 're-activated' by de-aeration of the solution and was able to introduce the same enantiomeric excess, as prior to the addition of oxygen was unaffected. It was found that not only cobalt(II) tetradentate complexes were useful in the ring-opening of meso 1,2-dioxines. Achiral iron(II) salen and ruthenium(II) salen were also made and shown to be capable of ring-opening the dioxine. A purchased chiral manganese(III) salen was also shown to be capable of ring-opening the 1,2-dioxine, however, the time taken for the rearrangement to occur led to ring closure of the gamma-hydroxy enone and dehydration of the cyclic hemiacetal. The catalysts were also applied to the enantioselective ring-opening of epoxy-1,2-dioxines for the first time with a high level of success with enantiomeric excesses of between 60 and 90 % introduced with most of the catalysts. To show that these catalysts have the potential for use in the synthesis of potentially bioactive cyclopropyl amino acids, amines, acids and alcohols a small number were prepared, including both racemic and optically enriched or optically pure cyclopropanes. / Thesis (Ph.D.)--School of Chemistry and Physics, 2003.

A series of new cobalt(II) beta-keto iminato complexes and cobalt(II) salens have been made and the effect of chirality in the northern, southern and peripheral quadrants of these catalysts, with respect to induced enantiomeric excess, during the ring-opening of 1,2-dioxines has been determined. Synthesis of a series of cobalt beta-keto iminato complexes was achieved after modification of literature procedures used for the synthesis of manganese beta-keto iminato complexes and this procedure was applied to generate ligands with ethyl, t-butyl, (-)-bornyl, (+)-menthyl and (-)-menthyl esters and a methyl side chain. Synthesis of the cobalt salens was also achieved using a modified literature procedure, in respect to the more complex aldehydes made. It was ascertained that chirality in the northern quadrant of these catalysts, obtained by the use of optically pure diamines, was of greatest importance in introducing enantiomeric excess into the products of ring-opening of 1,2-dioxines; namely gamma-hydroxy enones, and chirality in the southern and peripheral quadrants was of lesser, although still significant, importance. The reaction conditions were optimised and the conditions under which the highest enantiomeric excess was introduced were determined. The ideal solvent for the ring-opening was found to be THF with a catalyst concentration between 5 and 10 mol% at a temperature of -15oC. These conditions were found to be applicable to all catalysts and 1,2-dioxines tested. Enantiomeric excess as high as 76 % could be introduced when the optimised reaction conditions were used in large scale syntheses of cyclopropane (61). LC-MS studies indicate the presence of a solvent chelated species present in the reaction mixture when the solvent used is THF, however, the use of non-chelating solvents, such as dichloromethane, did not exhibit this same solvent chelated species. Catalyst dimers were also present in the mixture when analysed by LC-MS. The presence of oxygen in the reaction mixture was found to inhibit rearrangement of the dioxine with catalyst oxygen dimers (two molecules of catalyst bound to a single molecule of oxygen) present when analysed by LC-MS, however, the catalyst could be 're-activated' by de-aeration of the solution and was able to introduce the same enantiomeric excess, as prior to the addition of oxygen was unaffected. It was found that not only cobalt(II) tetradentate complexes were useful in the ring-opening of meso 1,2-dioxines. Achiral iron(II) salen and ruthenium(II) salen were also made and shown to be capable of ring-opening the dioxine. A purchased chiral manganese(III) salen was also shown to be capable of ring-opening the 1,2-dioxine, however, the time taken for the rearrangement to occur led to ring closure of the gamma-hydroxy enone and dehydration of the cyclic hemiacetal. The catalysts were also applied to the enantioselective ring-opening of epoxy-1,2-dioxines for the first time with a high level of success with enantiomeric excesses of between 60 and 90 % introduced with most of the catalysts. To show that these catalysts have the potential for use in the synthesis of potentially bioactive cyclopropyl amino acids, amines, acids and alcohols a small number were prepared, including both racemic and optically enriched or optically pure cyclopropanes. / Thesis (Ph.D.)--School of Chemistry and Physics, 2003.