The preparation, characterization and phenylacetylene polymerization of novel palladacycles

Joseph, Moegamat Cassiem (2016-03)

Thesis (MSc)--Stellenbosch University, 2016

Thesis

ENGLISH ABSTRACT : This thesis describes the synthesis and characterization of novel cationic palladacycles derived from various N-benzylidene-2,6-diisopropylaniline ligands and their use as catalysts in the polymerization of phenylacetylene. A series of N-benzylidene-2,6-diisopropylaniline ligands of general formula (2-R-C6H3)CH=N-(2,6-iPr2-C6H3), (R = H (L1); R = Cl (L2); R = Br (L3); R = F (L4); R = OMe (L5)) were prepared by the Schiff-base condensation reaction of 2,6-diisopropylaniline with the respective mono-substituted aldehyde in a 1:1 molar ratio. Reactions of ligands L1-L5 with (MeCN)2PdCl2 in a 1:1 molar ratio in the presence of NaOAc generated the dinuclear μ-Cl palladacycles (C1-C5) of the type [PdCl(R-C6H3)CH=N-{2,6-(iPr)2-C6H3}]2 (R = H (C1), Cl (C2), Br (C3), F (C4), OMe (C5)). The complexes were characterized by FT-IR-, 1H- and 13C{1H} NMR spectroscopy. The mononuclear neutral palladacycles of the type [Pd(PR’3)Cl(R-C6H3)CH=N{2,6-iPr2-C6H3}Cl] (PR’3 = PTA (C6-C10); PR’3 = PCy3 (C16-C20); PR’3 = PPh3 (C26-30)) were prepared by the cleavage of the μ-Cl palladacycles C1-C5 with two molar equivalents of the respective phosphine ligand. These complexes were fully characterized by FT-IR-, 1H-, 13C{1H}- and 31P{1H} NMR spectroscopy, ESI-MS spectrometry as well as elemental analysis. Single crystal X-ray diffraction analysis of complexes C8, C9, C18 and C30 confirmed that the geometry around the metal centre is slightly distorted square planar and that the coordination of the phosphine ligand is trans relative to the imine moiety. To generate the novel mononuclear cationic palladacycles, complexes C6-C10, C16-C20 and C26-C30 were subjected to chloride abstraction by NaBAr4 (Ar4 = 3,5-bis(trifluoromethyl)phenyl) in the presence of MeCN as coordinating solvent resulting in the cationic analogues with general formula [Pd(MeCN)(PR’3)(R-C6H3)CH=N-{2,6-(iPr)2-C6H3}]+ [B(Ar)4]- (PR’3 = PTA (C11-C15); PR’3 = PCy3 (C21-C25); PR’3 = PPh3 (C31-35)) being isolated as air- and moisture-stable solids. These complexes were characterized by FT-IR-, 1H-, 13C{1H}- and 31P{1H} NMR spectroscopy, ESI-MS spectrometry, elemental analysis and in the case of complexes C15 and C25 by single crystal X-ray diffraction. Spectroscopy data reveals that the coordination of the phosphine ligand to the metal centre remains trans relative to the imine moiety after coordination of the acetonitrile ligand. From the crystal structures of C15 and C25 it was observed that both complexes have a slightly distorted square planar geometry around the metal centre with the plane of the 2,6-diisopropylaniline moiety almost perpendicular to the plane of the endocycle ring. The reactivity of the novel cationic palladacycle complexes (C11-C15, C21-C25, C31-C35) towards phenylacetylene was evaluated. All complexes evaluated showed some degree of activity in phenylacetylene polymerization, with conversions ranging from 56 % to 95 %. A mixture of both cis-transoidal and trans-cisoidal polyphenylacetylene (PPA) were produced at room temperature with moderate molecular weights while the trans-cisoidal PPA can selectively be produced when the reactions are performed at slightly higher temperatures (60 °C). The nature of the ortho-substituent on the cyclometallated-ring had a marked effect on the efficiency of the catalysts with the highest conversion of 95 % being obtained for the complex with the most electron withdrawing substituent (C14). Increasing the steric bulk of the auxiliary phosphine ligand leads to higher molecular weight polyphenylacetylene being produced.

AFRIKAANSE OPSOMMING : Hierdie tesis beskryf die sintese, karakterisering en katalitiese aktiwiteit van nuwe kationiese palladasikliese komplekse afgelei vanaf verskillende N-bensilideen-2,6-diisopropielanilien ligande en die gebruik daarvan as katalisators in die polimerisering van fenielasetileen. ‘n Reeks N-bensilideen-2,6-diisopropielfenielamien ligande met die algemene formule (2-R-C6H3)CH=N-(2,6-iPr2-C6H3), (R = H (L1); R = Cl (L2); R = Br (L3); R = F (L4); R = OMe (L5)) is deur middel van ‘n Schiff-basis kondensasie reaksie van 2,6-diisopropielanilien met onderskeie monogesubstitueerde aldehiede in ’n 1:1 molêre verhouding berei. Reaksies van ligande L1-L5 met (MeCN)2PdCl2 in ‘n 1:1 molêre verhouding in die teenwoordigheid van NaOAc genereer die μ-Cl tweekernige palladasikliese komplekse (C1-C5) van die tipe [PdCl(R-C6H3)CH=N-{2,6- (iPr)2-C6H3}]2 (R = H (C1), Cl (C2), Br (C3), F (C4), OMe (C5)). Die komplekse is met FT-IR-, 1Hen 13C KMR spektroskopie gekarakteriseer. Die eenkernige neutrale palladasikliese komplekse van die tipe [Pd(PR’3)Cl(R-C6H3)CH=N{2,6- iPr2-C6H3}Cl] (PR’3 = PTA (C6-C10); PR’3 = PCy3 (C16-C20); PR’3 = PPh3 (C26-30)) is deur middel van die splitsing van die μ-Cl tweekernige palladasikliese komplekse C1-C5 met twee mol ekwivalent van die onderskeie fosfien ligande berei. Hierdie komplekse is volledig deur FT-IR-, 1H-, 13C{1H}- en 31P{1H} KMR spektroskopie, ESI-massa spektrometrie sowel as mikroanalise gekarakteriseer. Enkelkristal X-straal diffraksie analise van komplekse C8, C9, C18 en C30 bevestig dat die geometrie rondom the metaal effens verwronge vierkantvlakkig is en dat die koordinasie van die fosfien ligand trans relatief tot die imien gedeelte is. Ten einde nuwe eenkernige kationiese palladasikliese komplekse te vorm, is komplekse C6-C10, C16-C20 en C26-C30 met die chloried-abstraksiemiddel, NaBAr4 (Ar4 = 3,5- bis(trifluoormetiel)feniel) in die teenwoordigheid van MeCN as stabiliserende ligand, gereageer wat lei tot die kationiese analoë met algemene formule [Pd(MeCN)(PR’3)(R-C6H3)CH=N-{2,6-(iPr)2- C6H3}]+ [B(Ar)4]- (PR’3 = PTA (C11-C15); PR’3 = PCy3 (C21-C25); PR’3 = PPh3 (C31-35)) wat as stabiele vastestowwe geïsoleer is. Hierdie komplekse is deur FT-IR-, 1H-, 13C{1H}- en 31P{1H} KMR spektroskopie, ESI-massa spektrometrie, mikroanalise en in die geval van komplekse C15 en C25, deur enkelkristal X-straal diffraksie analise gekarakteriseer. Spektroskopie data bevestig dat die koordinasie van die fosfien ligand aan die metaal trans relatief tot die imien gedeelte bly na koordinasie van die asetonitriel ligand. Die kristal strukture van C15 en C25 toon aan dat beide komplekse ‘n effens verwronge vierkantvlak geometrie rondom die metaal het met die vlak van die 2,6-diisopropielanilien gedeelte wat amper loodreg tot die vlak van die endosikliese ring is. Die reaktiwiteit van die nuwe kationiese palladasikliese komplekse (C11-C15, C21-C25, C31-C35) teenoor fenielasetileen was geëvalueer. Alle komplekse wat in fenielasetileen polimerisasie geëvalueer was, het tot ‘n mate aktiwiteit vertoon met omsettings tussen 56 % en 95 %. ‘n Mengsel van beide cis-transoïed en trans-cisoïed polifenielasetileen was geproduseer by kamertemperatuur met matige molekulêre massas terwyl die trans-cisoïed polifenielasetileen selektief geproduseer word wanneer reaksies by 60 °C uitgevoer was. Die aard van die orto-substituent aan die siklometallerende-ring het ‘n merkbare uitwerking op die doeltreffendheid van die katalisators met ‘n omsetting van 95 % wat bereik is vir die kompleks wat die mees elektron-onttreking substituent het (C14). ‘n Verhoging in die steriese groote van die fosfien ligand het gelei tot die produksie van hoër molekulêre massa polifenielasetileen.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/98610
This item appears in the following collections: