Lactide polymerization with iron alkoxide complexes

Abstract

RésuméLes essais préliminaires pour préparer des alcoolates de fer à partir du bichlorure ou bibromure de fer (II), en les combinant avec des ligands de type diimino pyridine, ont engendré la formation de complexes homoleptiques et hétéroleptiques, dépendant des substituants sur les branches imines du ligand. Ces complexes homoleptiques octaédriques et paramagnétiques ont été étudiés par rapport à leurs propriétés spectroscopiques et cristallographiques. De plus, la synthèse des complexes de fer hétéroleptique a engendré de bons précurseurs penta-coordonnés pour les réactions de substitution de ligands avec des alcoolates de métaux alcalins, de manière à produire les dialcoolates de fer (II) désirés. Des techniques d'analyse telles que la spectroscopie UV-vis, l'analyse élémentaire, la spectrométrie de masse à haute résolution et la cristallographie aux rayons X ont été utilisées pour caractériser ces complexes de fer.L'activité catalytique de ces complexes de fer (II) a aussi été étudiée par rapport à la polymérisation du lactide; les dialcoolates convoités ont été générés in-situ en raison de la difficulté à produire et à isoler les dérivés alcoolates des complexes diimino pyridine de fer. Une étude approfondie a aussi été faite sur les réactions de polymérisation, surtout par rapport aux valeurs de conversion à l'échelle du temps, ainsi qu'à la tacticité des chaines de polymères obtenues. Ces analyses ont été effectuées par l'entremise de la spectroscopie de résonance magnétique nucléaire, de la chromatographie d'exclusion stérique, et de la spectrométrie de masse MALDI (désorption-ionisation laser assistée par matrice).Mots-clés: catalyseur de fer, polymérisation de lactide, ligands diiminopyridine, polymères biodégradables, chimie verte.iii AbstractInitial attempts to prepare iron alkoxide complexes, from iron (II) dichloride or dibromide, in combination with various bis(imino) pyridine ligands, led to the formation of homoleptic and heteroleptic complexes depending on the N-substituents on the imino moieties. A study was made of the resulting paramagnetic octahedral homoleptic complexes, with respect to their spectroscopic properties, as well as their crystallographic parameters. Alternatively, the synthesis of penta-coordinate heteroleptic iron (II) complexes provided good precursors for the ligand substitution reactions with alkaline alkoxides, to produce the desired iron bis (alkoxide) derivatives. Methods such as UV-vis spectroscopy, elemental analysis, high resolution mass spectrometry and X-ray crystallography were used for the characterization of these iron complexes.The catalytic activity of these iron (II) complexes was investigated with respect to lactide polymerization; the desired bis(alkoxide) species were generated in-situ due to the difficulties in isolating pure alkoxide derivatives of the bis(imino) pyridine iron (II) complexes. An informative study was made of both time-scale conversion values, as well as tacticity properties of the resulting polylactic acid chains, through proton nuclear...

Amides as Non-polymerizable Catalytic Adjuncts Enable the Ring-Opening Polymerization of Lactide With Ferrous Acetate Under Mild Conditions

“…The regular 72 m/z difference between ions showed that transesterification took place affecting the ester bond in a pure lactid diad. While transesterification in (co)polyesters based on dilactids has been observed for various catalysts, such as Sn(oct) 2 (Kowalski et al, 2005), DBU (Meyer et al, 2010) and a Fe(II)-based ROP catalyst (Keuchguerian et al, 2015), the extent is largely differing depending on the reaction conditions, especially the temperature and some transesterification catalysts do not promote the transesterification of the ester bond of the lactide unit (Lendlein et al, 2000). In most of the conducted syntheses, the area of the peaks representing species containing an even number of lactide units was roughly equal to peaks representing species with an odd number of lactide units.…”

Exploring the reactivity of manganese(iii) complexes with diphenolate-diamino ligands in rac-lactide polymerization

“…Most of the investigated catalyst systems are based on metals with an empty d-shell (group 1-4 and rare earth metals) 3,7,[13][14][15][16][17][18][19][20][21][22][23] or a filled d-shell (Zn, group 13-14). [4][5][6]11,14,15,24,25 Of catalysts based on mid-range transition metals, only iron [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] and copper [43][44][45][46][47][48][49][50][51][52][53][54] have been studied in somewhat more detail. Copper catalysts originally showed low to moderate activ...…”

Catalytic-Site-Mediated Chain-End Control in the Polymerization of rac-Lactide with Copper Iminopyrrolide Complexes

“…Mid- to late d n -transition metal complexes, on the other hand, have been sparingly studied. Very few studies investigated the performance of Cr, Mn, − or Co systems. ,, Next to iron, ,− copper complexes received the highest attention. − We have reported that copper diiminopyrrolide complex 1 polymerizes rac -lactide with an isoselectivity of P m = 0.7 at room temperature (Scheme ). Isoselective stereocontrol was unprecedented for copper complexes.…”