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Synthesis and Reactivity ResearchOnline@JCU This file is part of the following work: Hossain, Md Elius (2017) Lanthanoid formamidinates and halogenoaluminate complexes of the rare earths and alkaline earths: synthesis and reactivity. PhD Thesis, James Cook University. Access to this file is available from: https://doi.org/10.25903/5ccbcc1fc1876 Copyright © 2017 Md Elius Hossain The author has certified to JCU that they have made a reasonable effort to gain permission and acknowledge the owners of any third party copyright material included in this document. If you believe that this is not the case, please email [email protected] Lanthanoid formamidinates and halogenoaluminate complexes of the rare earths and alkaline earths; synthesis and reactivity A thesis submitted for the degree of Doctor of Philosophy by Md Elius Hossain M.Phil. (KUET), M.S. & B.Sc.(Hons) (DU) Bangladesh Discipline of Chemistry College of Science and Engineering James Cook University Townsville, Australia October 2017 Dedication This little effort is dedicated: To my beautiful mother, a strong and hardworking woman with a great vision. To the soul of my adoring younger brother Imdad (late), my true best friend. To my lovely wife, my best friend, my soulmate. “ইমদাদ, েতার ক থ া ম ে ন ক ে র আ ি ম � ি ত িনয়ত েচােখর পািন েগাপন করার বৃথা েচ�া কির ি ক � আ ম া র দ ে য় র য � ণ া িকছুেতই �শিমত হয় না। যিদও সমেয়র �েয়াজেন আমােক পথ চলেত হয়, হাসেত হয়, তবুও আিম েতার অনুপি�িত সবসময় অনুভব ক ি র ভ া ই । আ ম া র িব�াস, আ�া েতােক খুব শাি�েত েরেখেছন, ে দ া য় া ক ি র ে য খ া ে ন ই থ া ক ভ া ল থ া ক ।” ii Table of Contents Title………………………………………………………………………………………….i Dedication…………………………………………………………………………………..ii Table of Contents…………………………………………………………………………..iii Abstract…………………………………………………………………………………….vi Abbreviations……………………...……………………………………………………….ix Declaration………………………………………………………………………………….x Acknowledgements…………………………………...……...…………………………….xi CHAPTER 1 GENERAL INTRODUCTION 1.1 The rare earth elements………………………………………………………………….2 1.1.1 Occurrence and isolation..................................................................................2 1.1.2 Electronic configurations and oxidation states……………………………..7 1.1.3 The lanthanoid contraction……………………………………………………9 1.1.4 Coordination chemistry of lanthanoids……………………………………...11 1.1.5 Organometallic chemistry of lanthanoids……………………………………12 1.2 The alkaline earth elements……………………………………………………………12 1.2.1 Occurrence and isolation……………………………………………………13 1.2.2 Electronic configurations, oxidation states and properties………………….16 1.2.3 Uses of alkaline earth elements………………………………………………17 1.2.4 Organometallic chemistry of alkaline earth elements………………………..18 1.3 The ligands…………………………………………………………………………….18 1.3.1 Bulky ligands in rare earths organometallic chemistry……………………...19 1.3.2 Chemistry of the formamidinate ligands…………………..…………………20 1.3.3 Synthetic pathways………………………………………………….……….21 1.4 The current study………………………………………………………………………24 1.5 References……………………………………………………………………………..26 iii CHAPTER 2 CHEMISTRY OF HALOGENOALUMINATE LANTHANOID-ARENE COMPLEXES 2.1 Introduction………………………………………………………………………..…..33 2.2 Research Plan……………………………………………...………………………..…43 2.3 Results and Discussion……………………………………………………………..….44 2.3.1 Synthesis and Characterisation……………………………………………...44 2.3.2 X-ray Crystal Structures……………………………………………………..45 2.3.2.1 Iodoaluminate lanthanoid(III) complexes in toluene……………………...45 2.3.2.2 Iodoaluminate lanthanoid(II) complexes in toluene………………………55 2.3.2.3 Iodoaluminate lanthanoid(III) complexes in mesitylene………………..…65 2.3.2.4 Bromoaluminate lanthanoid(III) complexes in toluene……………..……..71 2.3.2.5 Bromoaluminate lanthanoid(II) complexes in toluene…………………….76 2.3.3 Catalysis for the Polymerisation of Isoprene……………………………...…79 2.3.4 Discussion…………………………………………………………………...81 2.4 Conclusions……………………………………………………………………………83 2.5 Experimental…………………………………………………………………………..84 2.6 X-ray crystal data………………………………………………………………………89 2.7 References……………………………………………………………………………..94 CHAPTER 3 CHEMISTRY OF HALOGENOALUMINATE ALKALINE EARTH-ARENE COMPLEXES 3.1 Introduction………………………………………………………………………..…101 3.2 Research Plan……………………………………………...…………………………115 3.3 Results and Discussion……………………………………………………………….116 3.3.1 Synthesis and Characterisation…………………………………………….116 3.3.2 X-ray Crystal Structures…………………………………………………....118 3.3.2.1 Iodoaluminate Ae(II) complexes in toluene…………………….………...118 3.3.2.2 Iodoaluminate Ae(II) complexes in mesitylene…………………………...127 iv 3.3.3 Discussion………………………………………………………………….134 3.4 Conclusions…………………………………………………………………..………134 3.5 Experimental……………………………………………………………………..…..135 3.6 X-ray crystal data…………………………………………………………………….137 3.7 References…………………………………………………………………..………..139 CHAPTER 4 FORMAMIDINATE CHEMISTRY OF DIVALENT AND TRIVALENT LANTHANOIDS 4.1 Introduction………………………………………………………………………..…149 4.2 Research Plan……………………………………………...…………………………173 4.3 Results and Discussion……………………………………………………………….174 4.3.1 Synthesis and Characterisation…………………………………………….174 4.3.2 X-ray Crystal Structures…………………………………………………....178 4.3.3 Discussion………………………………………………………………….191 4.4 Conclusions…………………………………………………………………..………192 4.5 Experimental……………………………………………………………………..…..193 4.6 X-ray crystal data……………………………………………………………………..199 4.7 References…………………………………………………………………..………..203 CHAPTER 5 CONCLUDING REMARKS Concluding Remarks……………………………………………………………………..207 References………………………………………………………………………………..211 APPENDICES 1 Related Chemistry with Relevance to This Thesis……………………………………...212 2 Experimental Procedures……………………………………………………………….222 3 Publications…………………………………………………………………………….227 v Abstract This thesis focuses on the synthesis and characterisation of halogenoaluminate π-arene complexes of rare earths and alkaline earths and compares the similarities between the two groups of metals. This thesis also discusses the reactivity of divalent rare earth N,N′- bis(aryl)formamidinate (ArForm) complexes. Study of the synthesis of halogenoaluminate π-arene complexes of rare earths has yielded 6 several new complexes containing η -arene, [Ln(arene)(AlX4)n] (Ln = La, Ce, Pr, Nd, Gd, Sm, Eu, Yb; arene = toluene, mesitylene; X = Br, I; n = 2, 3). Divalent compounds of Sm, Eu and Yb have lattice solvated toluene molecules; however, the trivalent complexes are 6 6 unsolvated. [Eu(η -MeC6H5)(AlI4)2]n.PhMe, [Yb(η -MeC6H5)(AlI4)2]n.1/2PhMe and 6 [Eu(η -MeC6H5)(AlBr4)2]n.PhMe are the first examples of polymeric structures among these complexes. All of the complexes have nine coordinated metal centres; however, the 6 2+ ytterbium complex [Yb(η -MeC6H5)(AlI4)2]n.1/2PhMe has an eight coordinate Yb centre, due to the lanthanoid contraction effect. The iodoaluminate and bromoaluminate complexes of lanthanoids were found to be isostructural and comparable with the chloroaluminate complexes in the literature. The Ln- X (X = Br, I), Ln-centroid and the average Ln-C bond distances in the divalent complexes are longer than that of the trivalent complexes. This was expected, as the divalent ions are larger than trivalent ions. Furthermore, the Ln-I distances in the iodoaluminate complexes are longer than the Ln-Br distances in the bromoaluminate complexes. These differences are associated with the larger ionic radii of Ln2+ and I- ions than the Ln3+ and Br- ions, respectively. The geometry of the complexes could be best described as distorted pentagonal bipyramidal, with the arene molecule at an axial position (the centroid-Ln-I/Br angles are close to the straight angle, 180o). The lanthanoid contraction was also evidenced by the gradual decrease of the Ln-X (X = Br, I), Ln-centroid and the average Ln-C bond distances in the trivalent complexes of lanthanoids (from lanthanum to gadolinium). This trend was also accessible among the divalent complexes from samarium to ytterbium, and there was an intense change in ytterbium as it is the smallest metal among the metals used for the synthesis here. The vi 6 catalytic activity of [Nd(η -C6H5Me)(AlI4)3] for isoprene polymerisation was performed at ambient temperature, and was less effective than the literature results of analogous chloroaluminate complexes. Investigation of the iodoaluminate π-arene complexes of alkaline earths (Ae) has given 6 several new complexes involving η -arene, [Ae(arene)m(AlI4)2] (Ae = Ca, Sr, Ba; arene = toluene, mesitylene; m = 1, 2). The Ca-centroid and the average Ca-C distances in the mesitylene complex were somewhat reduced than that of the toluene complex. This fact evidenced a stronger Ca-arene interaction in mesitylene complexes than in the toluene analogue, probably due to more electron donating effect of three methyl groups in mesitylene molecule than by one methyl group in toluene. Both complexes have a zigzag polymer structure. The strontium complex is isostructural with the samarium and europium complexes reported in chapter 2 due to their similar atomic radii. 4 The barium complex [(Ba(η -C6H5Me)2(AlI4)2] has the barium centre sandwiched between two toluene molecules both in an η4-fashion giving the barium centre an eight coordination. Nevertheless, the other complexes have only one arene molecule bonded to the metal centre. The Ba-I, Ba-C contacts are comparable with other analogous complexes considering the ionic radii of metals and iodide. Reactivity of divalent the formamidinate complexes [Yb(Form)2(thf)2] (Form = [RNCHNR]; R = 2,6-Me (XylForm); 2,4,6-Me (MesForm); 2,6-Et (EtForm); 2,6-iPr 2 3 2 2 (DippForm)) has been studied by using different oxidants such as Cl3CCCl3, BrCH2CH2Br and ICH2CH2I.
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