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Late transition metal complexes based on novel pyridine-triazole ligands as catalyst precursors in ethylene oligomerization and transfer hydrogenation reactions
Thesis (PhD)--Stellenbosch University, 2021
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| access_status_str | Open Access |
| author | Joseph, Moegamat Cassiem |
| author2 | Mapolie, Selwyn |
| author_browse | Joseph, Moegamat Cassiem Mapolie, Selwyn |
| author_facet | Mapolie, Selwyn Joseph, Moegamat Cassiem |
| author_sort | Joseph, Moegamat Cassiem |
| collection | Thesis |
| description | Thesis (PhD)--Stellenbosch University, 2021 |
| format | Thesis |
| id | oai:scholar.sun.ac.za:10019.1/124204 |
| institution | Stellenbosch University (South Africa) |
| language | en_ZA |
| last_indexed | 2026-06-10T12:45:52.267Z |
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| publishDate | 2021 |
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| source_str | SUNScholar — Stellenbosch University Repository |
| spelling | oai:scholar.sun.ac.za:10019.1/124204 Late transition metal complexes based on novel pyridine-triazole ligands as catalyst precursors in ethylene oligomerization and transfer hydrogenation reactions Joseph, Moegamat Cassiem Mapolie, Selwyn Swarts, Andrew Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. Metal complexes Palladium compounds Catalysis Ruthenium compounds Triazoles -- Reactivity UCTD Thesis (PhD)--Stellenbosch University, 2021 ENGLISH ABSTRACT: In this thesis, we describe the preparation and application of palladium- and ruthenium pyridyl-1,2,3-triazole complexes as catalyst precursors in the oligomerisation of ethylene as well as transfer hydrogenation reactions, respectively. A series of 1-substituted-4-pyridyl-1H-1,2,3-triazole ligands of general formula [(R2-C5H3N)C2HN3R1] (L1: R1 = octyl, R2 = H; L2: R1 = Ph, R2 = H; L3: R1 = 2,6-(Me)2Ph, R2 = H; L4: R1 = 4-phenol, R2 = H; L5: R1 = 4-(CF3)Ph, R2 = H; L6: R1 = octyl, R2 = Me; L7: R1 = 4-(CF3)Ph, R2 = Me; L8: R1 = 4-(CF3)Ph, R2 = Ph) were prepared via a microwave-assisted copper-catalysed alkyne-azide cycloaddition (CuAAC) between the appropriate aryl azide and alkyne derivative. The new ligands were fully characterised by a range of analytical techniques. Reactions of ligands, L1-L8, with (COD)PdMeCl, produced the new neutral palladium(II) methyl complexes [Pd(L1)MeCl] (C1); [Pd(L2)MeCl] (C2); [Pd(L3)MeCl] (C3); [Pd(L4)MeCl] (C4); [Pd(L5)MeCl] (C5); [Pd(L6)MeCl] (C6); [Pd(L7)MeCl] (C7) in excellent yields of 81-89 % (except in the case of C8 ([Pd(L8)MeCl]), which gave a 48 % yield). These complexes were characterized by FTIR and NMR spectroscopy, mass spectrometry and elemental analysis. Due to the asymmetrical nature of the complexes, the dominant isomer in solution and in the solid-state was unambiguously confirmed by 2D NMR spectroscopy as well as single-crystal x-ray analysis. The abstraction of the chlorido ligand by AgPF6 generated the cationic palladium(II)methyl complexes [Pd(L5)Me(MeCN)]PF6 (C9); [Pd(L7)Me(MeCN)]PF6 (C10); [Pd(L8)Me(MeCN)]PF6 (C11) ligated by the weakly coordinating solvent, MeCN. The cationic complexes were isolated in high yields (81-88 %) and fully characterized by a range of analytical techniques. The use of tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF) and pyridine as anion and coordinating solvent respectively generated a mixture of unstable-BArF adducts, irrespective of the reaction conditions employed. The reactivity of neutral palladium complexes (C1-C8) and cationic palladium complexes (C9-C11) towards ethylene oligo-/polymerisation, was evaluated. Complexes, C1-C5, upon activation with MAO as a co-catalyst, produced mainly butenes with small amounts of hexenes and traces of octenes detected. The incorporation of bulky groups on the pyridine ring led to a significant improvement in selectivity towards 1-butene (>90 %) for complexes, C6-C8. The catalyst activity of the complexes was dictated by the type of substituent on the triazole-ring. It was found that the more electron-withdrawing substituents such as CF3, enhances the electrophilicity of the metal centre, hence promoting monomer coordination and insertion. Comparable activities and selectivities were observed for the discrete cationic complexes, C9-C11, suggesting similarities in the nature of the active species for both classes of complexes. The reaction of ligands L1, L2 and L5 with [RuCl2(p-cymene)]2 in the presence of BPh4/PF6/BF4 salts, generated cationic half-sandwich ruthenium complexes, C12-C18, in excellent yields of 80 – 91 %. The complexes were characterized by FTIR- and NMR spectroscopy, mass spectrometry, elemental analysis and single crystal x-ray diffraction analysis. PGSE and NOE spectroscopy confirmed the existence of various types of ion-pairs in solution. It was found that C12 exists as quadruple ions (two sets of ion-pairs) in CHCl3, whereas contact ion-pairs was observed for C15 in CHCl3. However, solvent-separated ion-pairs were observed for C15 in MeCN. Conductivity measurements of C12 and C15 in 2-PrOH led to relatively low values resulting in the formation of contact ion-pairs although the dielectric constant of 2-PrOH is relatively higher than those of CH2Cl2 and CHCl3. The cationic half-sandwich ruthenium complexes (C12-C18) were evaluated as pre-catalysts in the transfer hydrogenation of selected ketones. Activation of the complexes with KOH generated efficient catalysts that transformed acetophenone to 1-phenylethanol in moderate to excellent conversions (56 - 99 %) after 6 hours using low catalyst- and base loadings of 0.1 mol% and 2 mol% respectively. The type of anion employed had a marked effect on the reactivity of the complexes. Regardless of the substituent on the triazole ring, the complexes containing the smaller PF6 and BF4 anions were found to be more active in catalysing the transfer hydrogenation reactions. The decreased activity was ascribed to the extent of ion-pairing that exists between the anion and cation in 2-PrOH for these catalysts. Essentially greater ion-pairing leads to a decrease in catalytic activity. The efficiency of complex C15 was further highlighted by its ability to tolerate a small library of carbonyl substrates with conversions between 70-99 % observed. Preliminary mechanistic studies were performed and a metal-hydride species was detected by high-resolution mass spectrometry. Based on the results obtained, a plausible mechanism is proposed. AFRIKAANS OPSOMMING: In hierdie tesis word die sintese, karakterisering en toepassing van palladium en ruthenium piridiel-1,2,3-triazool komplekse beskryf as katalisators in die oligomerisering van etileen sowel as oordraghidrogeneringsreaksies. ‘n Reeks van ariel-gesubstitueerde 1,2,3-triasool-piridien ligande met die algemene formule [(R2-C5H3N)C2HN3R1] (L1: R1 = octyl, R2 = H; L2: R1 = Ph, R2 = H; L3: R1 = 2,6-(Me)2Ph, R2 = H; L4: R1 = 4-fenol, R2 = H; L5: R1 = 4-(CF3)Ph, R2 = H; L6: R1 = oktiel, R2 = Me; L7: R1 = 4-(CF3)Ph, R2 = Me; L8: R1 = 4-(CF3)Ph, R2 = Ph) was berei deur ‘n mikrogolf-ondersteunde koper-gekataliseerde alkyn-asied sikloaddisie (CuAAC) reaksie tussen die toepaslike arielazied en alkyn afgeleide. Die nuwe ligande was volledig gekarakteriseer deur ‘n verskeidenheid analitiese tegnieke. Reaksies van ligande, L1-L8, met (COD)PdMeCl vorm nuwe neutrale palladium(II)metiel komplekse [Pd(L1)MeCl] (C1); [Pd(L2)MeCl] (C2); [Pd(L3)MeCl] (C3); [Pd(L4)MeCl] (C4); [Pd(L5)MeCl] (C5); [Pd(L6)MeCl] (C6); [Pd(L7)MeCl] (C7) in uitstekende opbrengste van 81 – 89 % (behalwe in die geval van C8 ([Pd(L8)MeCl]), wat 48 % opbrengs lewer). Hierdie komplekse was deur FTIR- en NMR spektroskopie, massaspektrometrie en elementêre analiese gekarakteriseer. As gevolg van die asimmetriese aard van die komplekse, is die dominante isomeer in beide die oplossing- en vaste toestand bevestig deur 2D NMR spektroskopie sowel as enkelkristal X-straal diffraksie analiese. Die abstraksie van die chloriedligand deur AgPF6 het die kationiese palladium(II)metiel komplekse [Pd(L5)Me(MeCN)]PF6 (C9); [Pd(L7)Me(MeCN)]PF6 (C10); [Pd(L8)Me(MeCN)]PF6 (C11) wat deur MeCN geligeer is, as die swak-koördinerende oplosmiddel gegenereer. Die kationiese komplekse is in hoë opbrengste (81-88 %) geïsoleer en volledig gekarakteriseer deur 'n verskeidenheid analitiese tegnieke. Ongeag van die reaksie kondisies,word ‘n mengsel van onstabiele tetrakis[3,5-di(trifluorometiel)feniel]boraat-addukte (BArF-addukte) verkry wanneer BArF en piridien as anioon en gekoördinerende oplosmiddel onderskeidelik gebruik was. Die reaktiwiteit van die neutrale palladiumkomplekse (C1-C8) en kationiese palladiumkomplekse (C9-C11) was ‘n etileen oligo-/polimerisasie geëvalueer. Komplekse, C1-C5, het hoofsaaklik buteen geproduseer,met klein hoeveelhede van hekseen en okteen na aktivering met MAO as mede-katalisator. Die inlywing van groot groepe in die piridien ring het tot ‘n aansienlike verbetering in die selektiwiteit teenoor 1-buteen (> 90%) vir komplekse, C6-C8, gelei. Die katalisatoraktiwiteit van die komplekse was bepaal deur die tipe substituent op die triazoolring. Daar was gevind dat die meer elektronontrekkende substituente soos CF3, die elektrofiliteit van die metaal verhoog en bevorder sodoendemonomer koördinasie en invoeging. Vergelykbare aktiwiteite en selektiwiteite is waargeneem vir die diskrete kationiese komplekse, C9-C11, wat ooreenkomste in die aard van die aktiewe spesie vir beide klasse komplekse voorstel. Die reaksie van ligande L1, L2 en L5 met [RuCl2(p-cymene)]2 in die teenwoordigheid van BPh4/PF6/BF4 soute, het die kationiese halfbroodjie-ruthenium komplekse gegenereer, C12-C18, in uitstekende opbrengste van 80–91 %. Die komplekse was gekarakteriseer deur FTIR- en NMR-spektroskopie, massaspektrometrie, elementêre analiese en enkelkristal X-straal diffraksie analiese. PGSE- en NOE-spektroskopie het die bestaan van verskillende soorte ioonpare in oplossing bevestig. Daar is gevind dat C12 bestaan uit viervoudige-ione (twee stelle ioonpare) in CHCl3, terwyl kontak ioon-pare waargeneem was vir C15 in CHCl3. Inteendeel, oplosmiddel-geskeide ioon-pare was waargeneem vir C15 in MeCN. Geleidingsmetings van C12 en C15 in 2-PrOH het gelei tot relatiewe lae waardes wat tot die vorming van kontak ioon-pare gelei het, alhoewel die diëlektriese konstante van 2-PrOH relatief hoër is as dié van CH2Cl2 en CHCl3. Die kationiese halfbroodjie-rutenium komplekse (C12-C18) was as katalisators geëvalueer in die oordraghidrogenasie van geselekteerde ketone. Aktivering van die komplekse met KOH het doeltreffende katalisators genereer wat asetofenoon na 1-fenieletanol in matige tot uitstekende opbrengste omgeskakel het (56–99 %) na 6 ure met lae katalisator- en basis laaiings van onderskeidelik 0,1 mol% en 2 mol%. Die tipe anioon wat gebruik is, het 'n duidelike uitwerking op die reaktiwiteit van die komplekse gehad. Ongeag van die substituent op die triazoolring, was daar gevind dat die komplekse wat die kleiner PF6- en BF4-anione bevat, meer aktief was in die oordraghidrogeneringsreaksies. Die verminderde aktiwiteit word toegeskryf aan die mate van ioon-paring wat bestaan tussen die anioon en die katioon in 2-PrOH vir hierdie katalisators. Dus het 'n groter ioonparing gelei tot verminderde katalitiese aktiwiteit. Die doeltreffendheid van kompleks C15 is verder beklemtoon deur die vermoë om 'n klein groep karboniel substrate om te skakel met ‘n opbrengs tussen 70-99%. Voorlopige meganistiese studies is uitgevoer en 'n metaalhidried spesie is deur hoë resolusie massaspektrometrie geidentifiseer. Op grond van hierdie resultate, word 'n gepaste meganisme voorgestel. Doctorate 2021-07-23T21:08:41Z 2022-02-22T10:16:29Z 2022-02-23T03:00:14Z 2021-12 Thesis http://hdl.handle.net/10019.1/124204 en_ZA xxxii, 185 pages : illustrations application/pdf |
| spellingShingle | Metal complexes Palladium compounds Catalysis Ruthenium compounds Triazoles -- Reactivity UCTD Joseph, Moegamat Cassiem Late transition metal complexes based on novel pyridine-triazole ligands as catalyst precursors in ethylene oligomerization and transfer hydrogenation reactions |
| title | Late transition metal complexes based on novel pyridine-triazole ligands as catalyst precursors in ethylene oligomerization and transfer hydrogenation reactions |
| title_full | Late transition metal complexes based on novel pyridine-triazole ligands as catalyst precursors in ethylene oligomerization and transfer hydrogenation reactions |
| title_fullStr | Late transition metal complexes based on novel pyridine-triazole ligands as catalyst precursors in ethylene oligomerization and transfer hydrogenation reactions |
| title_full_unstemmed | Late transition metal complexes based on novel pyridine-triazole ligands as catalyst precursors in ethylene oligomerization and transfer hydrogenation reactions |
| title_short | Late transition metal complexes based on novel pyridine-triazole ligands as catalyst precursors in ethylene oligomerization and transfer hydrogenation reactions |
| title_sort | late transition metal complexes based on novel pyridine triazole ligands as catalyst precursors in ethylene oligomerization and transfer hydrogenation reactions |
| topic | Metal complexes Palladium compounds Catalysis Ruthenium compounds Triazoles -- Reactivity UCTD |
| url | http://hdl.handle.net/10019.1/124204 |
| work_keys_str_mv | AT josephmoegamatcassiem latetransitionmetalcomplexesbasedonnovelpyridinetriazoleligandsascatalystprecursorsinethyleneoligomerizationandtransferhydrogenationreactions |