The use of mononuclear and multinuclear complexes of rhodium and ruthenium in catalytic olefin hydroformylation and hydroaminomethylation reactions

Date
2020-03
Journal Title
Journal ISSN
Volume Title
Publisher
Stellenbosch : Stellenbosch University
Abstract
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).
AFRIKAANSE OPSOMMING: 'n Reeks imino-pyridien ligande (L1-L8) was gesintetiseer deur middel van Schiff-basis kondensasie reaksies. Hierdie ligande was vervolgens aan Rh(I) en Ru(II) gekomplekseer, deur gebruik te maak van [Rh(COD)Cl]2 en [RuCl2(p-cymene)]2, om vyf nuwe Rh(I) (C1-C5) en drie nuwe Ru(II) (C6-C8) imino-pyridien komplekse te vorm. Die rhodium komplekse bevat beide elektron-onttrekkende (F) en elektron-donerende groepe (CH3 en OH). In die geval van die Ru(II) komplekse, was C6 en C7 mono-kernagtig van aard, terwyl C8 bi-nukluêr is. Hierdie komplekse was volledig gekarakteriseer deur van 'n reeks analitiese tegnieke gebruik te maak. Dit sluit in IR en KMR (1H en 13C) spektroskopie, massaspektrometrie, elementêre analiese en die bepaling van hul smeltpunte. Die Rh(I) komplekse (C1-C4) was daarna geëvalueer as katalisator-voorlopers in die hidroformulering van 1-okteen. Na 'n reaksietyd van slegs 1 uur was die volledige omskakeling van 1-okteen bereik, maar lae chemoselektiwiteite ten opsigte van aldehiede was verkry (~52 %) by 30 bar CO:H2 (1: 1), 0,05 mol% katalisator-lading en 75 °C, met geringe regioselektiwiteit teenoor die lineêre aldehiede (58%). Die effek van druk was dus verder geëvalueer. Met ‘n verlaging in druk vanaf 30 na 10 bar het die opbrengs van aldehiede verder gedaal. Hoë chemoselektiwiteit ten opsigte van aldehiede (~75 %) was verkry met ‘n verlaging in temperatuur vanaf 75 na 55 °C, al was dit teen matige omskakelings (~49 %) van die substraat. Dit het ook 'n toename in die regioselektiwiteit teenoor die lineêre aldehied (70%) teweeg gebring. Die R-groepe (F, CH3, OH) het geen noemenswaardige uitwerking op die katalitiese aktiwiteit gehad nie. Die hidroformulering van 2-okteen was ook uitgevoer en het soos verwag getoon dat die hidroformulering van interne alkene baie stadiger is as terminale alkene. Die hidroformulering van 1-okteen was ook met behulp van ‘n singas-surrogaat, formaldehied, probeer. Geen aldehidiese produkte was egter verkry nie, aangesien die 1-okteen isomerisering na interne alkene (~80 %) en hidrogenering na oktaan (~20 %) ondergaan het. Die rhodium komplekse, C4 en C5 was daarna as katalisator-voorlopers in die hidroaminometielering van 1-okteen in die teenwoordigheid van amiene (piperidien, anilien en bensielamien) gebruik. Hoë chemoselektiwiteite ten opsigte van N-alkielpiperidiene is verkry (~80 %) by 30 bar CO:H2 (1:1), 0,1 mol% katalisator-lading, 75 °C en 2 uur, waar die lineêre amien met 75 % selektiwiteit vorm. Die hidroaminometielering aktiwiteit van C4 en C5 was beter as die van die wel-bekende kompleks, HRhCO(PPh3)3. Die uitvoering van die hidroaminometielering reaksie in die teenwoordigheid van 'n oormaat piperidien het die katalitiese aktiwiteit positief beïnvloed, aangesien hoër omskakelings en opbrengste van amiene verkry was. Op die oog af verhoed piperidien newe-reaksies, soos die isomerisering en hidrogenering van 1-okteen gedeeltelik. Die invloed van druk en temperatuur was ook ondersoek en dit het die chemoselektiewe sintese van N-alkielpiperidiene (~90 %) teweeg gebring by 30 bar CO: H2 (1: 1), 0,1 mol% katalisator-lading, 2 uur reaksie tyd en 85 ° C. Die fokus was daarna verskuif na die gebruik van ‘n primêre amien, anilien. Die reaksie kondisies wat geoptimiseer was vir die hidroaminometielering van 1-okteen in die teenwoordigheid van piperidien (30 bar CO:H2 (1:1), 0,1 mol%, 1 uur en 85 ° C) was gekies as die aanvanklike kondisies. As gevolg van die laer basisiteit van anilien in vergelyking met die van piperidien, was die opbrengs van die N-gealkieleerde aniliene aanvanklik laag, alhoewel al die 1-okteen heeltemal omgeskakel was. Die reaksie kondisies moes geoptimiseer word om die opbrengste van die N-alkieleerde aniliene te verhoog. Ons het spesifiek gefokus op die gedeeltelike druk van H2. Met behulp van 'n 1:3 verhouding van CO:H2 (50 bar) en ‘n reaksietyd van 6 uur kon sekondêre amiene in ~45 % opbrengs gesintetiseer word. Uitvoering van die hidroaminometielering reaksie in die teenwoordigheid van oormaat anilien (1,5 ekw.), kon N-alkieleerde aniliene chemoselektief (~95 %) gesintetiseer word, alhoewel teen matige regioselektiwiteit na die lineêre amien (56 %). In die gebruik van bensielamien in die hidroaminometielering van 1-okteen, was die reaksie aansienlik vinniger in vergelyking met die gebruik van anilien. Dit word toegeskryf aan die hoër basisiteit en dus die hoër nukleofilisiteit van bensielamien. N-gealkieleerde bensielamiene was dus chemoselektief gesintetiseer, alhoewel teen matige regioselektiwiteit na die lineêre amien. Die Ru(II) komplekse, C6-C8, was ook geëvalueer as katalisator-voorlopers in die hidroaminometielering van 1-okteen in die teenwoordigheid van bensielamien. Alhoewel hierdie komplekse effens hoër temperature (110 °C) benodig in vergelyking met rhodium, bemiddel hulle ook die hidroaminometielering van 1-okteen met bensielamien doeltreffend. Tydens die hidroaminometielerings reaksie was die aldehiede tussenprodukte nooit waargeneem nie, alhoewel alkene (terminaal en intern) nog teenwoordig was. Dit dui daarop dat die hidroformuliserings reaksie vir hierdie ruthenium komplekse stadiger is as die reduktiewe aminering reaksie. Die potensiaal van hidroaminometielering in die sintese van waardevolle chemikalieë was ook getoon. In hierdie opsig was hidroaminometielering gebruik om primêre amiene in hoë opbrengste te sintetiseer vanaf goedkoop olefien voermiddels. Deur gebruik te maak van dieselfde metodologie, is dopamien-analoë van eugenol gesintetiseer. Die sintese van biopolymeer-voorlopers is ook gedemonstreer deur middel van die hidroaminometielering van metiel-10-undesenoaat in die teenwoordigheid van amino suur esters (L-prolien-metielester en metiel piperidien-4-karboksilaat). Die hidroaminometielering van 1-okteen met hierdie amino suur esters het toegang gegee tot bio-surfaktante. Daar was gevind dat die pirrolidiel- en piperidiel-groepe bydra tot die hidrofobisiteit van die alkielketting. Ons het ook gevind dat die posisie van die hydrofiliese groep relatief tot die alkielketting ook die kritieke misel konsentrasie (CMC) kan beïnvloed.
Description
Thesis (PhD)--Stellenbosch University, 2020.
Keywords
Hydroaminomethylation, Hydroformylation, Olefins, Rhodium, Ruthenium
Citation