Browsing by Author "October, Jacquin"
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- ItemNovel multinuclear complexes of Rh and Ru and their application in alkene hydroformylation(Stellenbosch : Stellenbosch University, 2015-11-25) October, Jacquin; Mapolie, Selwyn Frank; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: This project entailed the synthesis and characterization of mono- and multi-nuclear rhodium and ruthenium iminopyridyl complexes and their application in the hydroformylation of 1- octene. The multi-nuclear complexes were synthesized in order to investigate whether it could produce catalysts with higher activity than their mononuclear analogues. Four novel iminopyridyl ligands, ranging from mono- to tetra-functional compounds, were synthesized. The synthesis was a two-step process initially involving a Schiff base condensation reaction between 2-pyridinecarboxaldehyde and 4-aminophenol to produce a hydroxy functionalized pyridine-imine. The latter was then subjected to a nucleophilic substitution reaction with an appropriate benzyl bromide derivative to yield the target ligands. All these ligands were isolated in moderate to good yields and characterized using a range of analytical techniques. These ligands, together with the hydroxy functionalized pyridine imine, were then complexed to both Rh(I) and Ru(II) metal precursors, yielding ten novel metal complexes. The characterization of some of the complexes, especially the multi-nuclear complexes, were slightly more difficult due to their low solubility. However, all these complexes could be isolated in good to high yields as stable green-brown (in the case of Rh(I)) and yellow-orange (in the case of Ru(II)) solids. Finally, these complexes were applied as catalyst precursors in the hydroformylation of 1- octene. In the case of the Rh(I) complexes, relatively high activities were observed, with conversions ranging between 50 – 90 % in all cases, when tested at 30 bar, 75 °C and a 0.05 mol% catalyst loading. The activity was found to increase when going from the mono- to the bi-nuclear catalyst. However, solubility in the reaction medium was a major issue for the trinuclear catalyst, as it contributed to the lower activity observed. High chemoselectivity towards aldehydes was observed for all catalysts, which increased with reaction times. During shorter reaction time, linear regioselectivity was also relatively high. This however, decreased with increasing reaction time as the internal octenes formed initially, were converted to branched aldehydes. When the Ru(II) complexes were tested under the same conditions as the Rh(I) complexes, very low activity was observed. Under more stringent conditions (45 bar, 120 °C, 0.5 mol%) the ruthenium catalysts performed relatively well, compared to other complexes in the literature. The same trend in terms of the chemo- and regioselectivity for the Ru(II) complexes were observed. The Rh(I) complexes were far more active than the Ru(II) complexes.
- ItemThe use of mononuclear and multinuclear complexes of rhodium and ruthenium in catalytic olefin hydroformylation and hydroaminomethylation reactions(Stellenbosch : Stellenbosch University, 2020-03) October, Jacquin; Mapolie, Selwyn Frank; Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science.ENGLISH ABSTRACT: A range of imino-pyridine ligands (L1-L8) were synthesized via Schiff-base condensation reactions. These ligands were subsequently complexed to Rh(I) and Ru(II) using [Rh(COD)Cl]2 and [RuCl2(p-cymene)]2, to form five novel Rh(I) (C1-C5) and three novel Ru(II) (C6-C8) imino-pyridine complexes. The rhodium complexes contained both electron-withdrawing (F) and electron-donating groups (CH3 and OH). In the case of the Ru(II) complexes, C6 and C7 were mononuclear in nature while C8 was binuclear. These complexes were fully characterized using a range of analytical techniques, including IR and NMR (1H and 13C) spectroscopy, mass spectrometry, elemental analysis and melting point measurements. The Rh(I) complexes (C1-C4) were evaluated as catalyst precursors in the hydroformylation of 1-octene. Full conversion of 1-octene was achieved after only 1 h reaction time, however, poor chemoselectivities towards aldehydes were obtained (only ~52 %) at 30 bar CO:H2 (1:1), 0.05 mol% catalyst loading and reaction temperature of 75 °C, with slight regioselectivity towards the linear aldehyde (58 %). Therefore, the effect of pressure was evaluated. However, as the pressure was decreased from 30 to 10 bar, the yield of the aldehydes decreatowards the aldehydes (~75 %) was obtained when the temperature was decreased from 75 to 55 °C, albeit at moderate conversions (~49 %) of the substrate. This also produced an increase in the regioselectivity towards the linear aldehyde (70 %). The R groups (F, CH3, OH) had no significant effect on the catalytic activity. The hydroformylation of 2-octene was also performed which showed as expected that the rate of hydroformylation of internal olefins is much slower than that of terminal olefins. The hydroformylation of 1-octene was also attempted using a syngas surrogate, such as formaldehyde. However, no aldehydic products were obtained since with 1-octene. Isomerization to internal olefins (~80 %) and hydrogenation to octane (~20 %) were detected. The rhodium complexes, C4 and C5 were then used as catalyst precursors in the hydroaminomethylation of 1-octene in the presence of amines (piperidine, aniline and benzylamine). High chemoselectivities towards N-alkyl piperidines were obtained (~80 %) at 30 bar CO:H2 (1:1), 0.1 mol% catalyst loading, 75 °C and 2 h, forming the linear amine in 75 % selectivity. The hydroaminomethylation activity of C4 and C5 was found to be superior to that of the well-known complex, HRhCO(PPh3)3. Performing the hydroaminomethylation reaction in the presence of excess piperidine, dramatically influenced the catalytic activity since higher conversions and yields of amines were obtained. Piperidine appears to partially inhibit side reactions such as the isomerization and hydrogenation of 1-octene. The influence of pressure and temperature was also investigated and it was observed that this promoted the chemoselective synthesis of N-alkyl piperidines (~90 %) at 30 bar CO:H2 (1:1), 0.1 mol % catalyst loading, 2 h and 85 °C. The focus was then shifted to the use of primary amine, aniline, as co-reagent in the hydroaminomethylation reaction. The initial reaction conditions were chosen as those optimized for the hydroaminomethylation of 1-octene in the presence of piperidine (30 bar CO:H2 (1:1), 0.1 mol%, 1 h, and 85 °C). As a result of the lower basicity of aniline in comparison to piperidine, the yield of the N-alkylated anilines were initially low, even though 1-octene was completely consumed during the reaction. The reaction conditions had to be optimized in order to increase the yield of the N-alkylated anilines. We specifically focussed on the partial pressure of H2. Using a 1:3 ratio of CO:H2 (50 bar) and extending the reaction time to 6 h, secondary amines could be synthesized in ~45 % yield. When the hydroaminomethylation reaction was performed in the presence of excess aniline (1.5 eq), N-alkylated anilines could be synthesized chemoselectively (~95 %), albeit at moderate regioselectivity towards the linear amine (56 %). Using benzylamine in the hydroaminomethylation of 1-octene, the reaction was significantly faster in comparison to the use of aniline. This was attributed to the higher basicity and thus higher nucleophilicity of benzylamine. N-alkylated benzylamines were thus also synthesized chemoselectively while also proceeding at moderate regioselectivities. The Ru(II) complexes, C6-C8, were also evaluated as catalyst precursors in the hydroaminomethylation of 1-octene in the presence of benzylamine. Although these complexes require slightly higher temperatures (110 °C) in comparison to rhodium, they also efficiently mediate the hydroaminomethylation of 1-octene with benzylamine. During the hydroaminomethylation reaction, aldehyde intermediates were not observed even when there were still unreacted olefins (terminal and internal) present in the reaction mixture. This suggest that the hydroformylation reaction is slower than the reductive amination reaction for these ruthenium complexes. The potential of hydroaminomethylation in the synthesis of value-added chemicals was also demonstrated. In this regard, hydroaminomethylation was used to synthesize primary fatty amines in high yields from cheap olefin feedstocks. Using a similar methodology, dopamine-analogues were synthesized from eugenol. The synthesis of bifunctional biopolymer precursors was also demonstrated via the hydroaminomethylation of methyl 10-undecenoate in the presence of amino acid esters (L-proline methyl ester and methyl piperidine-4-carboxylate). The hydroaminomethylation of 1-octene with these amino acid ester provided access to biosurfactants. It was found that the pyrrolidyl and piperidyl moieties contribute towards the hydrophobicity of the alkyl chain. We also found that the position of the hydrophilic group relative to the alkyl chain can also influence the critical micelle concentration (CMC).