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The work presented in this thesis discusses the formation and behaviour of a variety of different ArForm rare-earth complexes using five ArForm ligands of varied functionalities (N,N'-bis(Aryl)Formamidine: Aryl = 2,6-difluorophenyl (DFFormH), 2,6-diisopropylphenyl (DippFormH), 4-methyl phenyl (p-TolFormH), and 2-trifluoromethylphenyl). In addition the chemistry of rare-earth 3,5-dimethylpyrazolate (Me2pz) complexes is also discussed. The majority of divalent rare-earth ArForm complexes known have been synthesised by redox transmetallation protolysis (RTP) protocols or salt metathesis in THF. Chapter two examines two different synthetic approaches to form divalent rare-earth N,N'-bis(2,6-difluorophenyl)formamidinate DFForm complexes. Initially complexes were generated by the RTP method utilising three different solvent media (THF, PhMe, and Et2O), where the oxidation state of the resulting complex was dependent on the solvent used. Additionally treatment of DFFormH with Ln0 metals in CH3CN proved to be an effective synthetic route to divalent DFForm complexes for both Eu and Yb. However, when the direct metal synthetic method was extrapolated to the bulky DippForm ligand system, results were varied. Although the reactivity of divalent [Sm(DippForm)2(thf)2] has been studied under a variety of conditions (Scheme 1.6), currently the isostructural ytterbium analogue ([Yb(DippForm)2(thf)2]), has only been treated with halogenating oxidants.[58f] Chapter Three investigates the ability for the DippForm ligands to stabilise metal ketyl complexes generated by treating [Yb(DippForm)2(thf)2] with a variety of different aromatic ketones and 1,2-diketones. Through a single electron redox process, a variety of ketyl complexes was generated and showed interesting structures and reactivity.Although divalent and trivalent ArForm complexes are known, tetravalent species have remained an unexplored area. Chapter Four discusses the synthesis and oxidation of five novel cerium(III) ArForm complexes by trityl chloride, leading to transient cerium(IV) species that were prone to rapid decomposition. A cerium(IV) ArForm complex was successfully generated by an alternative method, namely protolysis reactions between ArFormH and tetravalent cerium silylamides. Some of the work presented in this Chapter has been recently published and these publications are in Appendix A and Appendix B.In the final chapter on ArForm ligands, Chapter Five, the coordination of N,N'-bis(2-trifluoromethylphenyl)formamidinate to rare-earth ions is discussed. It was initially hypothesised that the CF3 group would coordinate to the rare-earth metal centre and then undergo C-F activation to produce rare-earth heteroleptic fluoride complexes. However, surprisingly, the CF3 group underwent complete de-fluorination, producing inorganic fluorides and also poly(trifluoromethylphenyl)amidines. This unexpected result is discussed in terms of the conditions of activation along with the role of the rare-earth element. Chapter Six ventures away from the chemistry of rare-earth formamidinates and discusses the chemistry of rare-earth 3,5-dimethylpyrazolate complexes in terms of structures and their peculiar reactivity, where it appears that these complexes have a high affinity to form oxide cages. Part of this work has been recently published and is presented in Appendix C. Across these Chapters the versatility of rare-earth formamidinate complexes has been demonstrated, with new binding modes to rare-earths identified, new synthetic methods determined, different types of reactivity investigated, and the results have opened the doors to much exciting new chemistry.
Reliable transformation of low-cost rare-earth metal oxides to organometallic rare-earth metal complexes is a prerequisite for the advancement of non-aqueous rare-earth metal chemistry. We have recently developed an in situ method to prepare rare-earth alkyl and halide precursors supported by a diamidoferrocene NNfc, 1,1'-fc(NSiMe2Bu)2, as an ancillary ligand. We extended the scope of this method to other lanthanide ions including those that are redox active, such as cerium, praseodymium, samarium, terbium, thulium, and ytterbium. Specifically, samarium trisbenzyl could be generated in situ and then converted to the corresponding samarium benzyl or iodide complexes in good yield. However, it was found that ytterbium trisbenzyl could not be formed cleanly and the consequent conversion to ytterbium iodide complex was low yielding. By adapting an alternative route, the desired ytterbium chloride precursor could be obtained in good yield and purity. The synthesis and characterization of two yttrium alkyl complexes supported by a bisphosphinimine ferrocene ligand, NPfc (1,1 -di(2,4-di-tert-butyl-6-diphenylphosphiniminophenoxy)ferrocene), were accomplished. Although (NPfc)Y(CH2Ph) and (NPfc)Y(CH2SiMe3) could be structurally characterized, these compounds are thermally sensitive and decompose at ambient temperature within hours. Their characterization was accomplished by NMR spectroscopy, electrochemical measurements, and elemental analysis. Reactivity studies were also carried out; however, the lack of prolonged thermal stability at ambient temperature of these molecules led to decomposition before a clean transformation to reaction products could be observed. The synthesis and characterization of Ln-C4Ph4-K, [(NNTBS)Ln( 2-C4Ph4)][K(THF)x] (Ln = Sc, Y, Lu), rare-earth metal complexes supported by a ferrocene diamide ligand, NNTBS (NNTBS = fc(NSitBuMe2)2, fc = 1,1 -ferrocenediyl), were accomplished. The preparation of the half-sandwich compounds, Ln-naph-K, [(NNTBS)Ln( -C10H8)][K(THF)2] (Ln = Sc, Y, Lu, La), was necessary in order to obtain high yields of rare-earth metallacyclopentadienes. Unlike Y and Lu, La did not show the same reactivity toward PhCCPh. The characterization of the new metal complexes was accomplished by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction.
During the last 30 years, knowledge of the essential role that pyrrole structures play in the chemistry of living organisms, drug design, and the development of advanced materials has increased. Correspondingly, research on the diverse issues of synthetic, theoretical, and applied chemistry has snowballed. Devoted to the latest achievements of this field, Chemistry of Pyrroles covers the discovery and development of a novel, facile, and highly effective method for the construction of the pyrrole ring from ketones (ketoximes) and acetylene in superbase catalytic systems (Trofimov reaction). It provides cutting-edge details on the preparation of valuable but previously inaccessible pyrrole compounds. It includes approximately 1,000 structures of novel pyrrole compounds, their yields, and physical-chemical characteristics. The authors analyze conditions of typical syntheses, limitations of their applicability, and possibility of vinyl chloride or dichloroethane application instead of acetylene. They examine chemical engineering aspects of the first synthesis of tetrahydroindole and indole from commercially available oxime of cyclohexanone and acetylene. In addition, the book discusses new facets of pyrroles and N-vinyl pyrroles reactivity in the reactions with the participation of both the pyrrole ring and N-vinyl groups. The book provides condensed, clear-cut information on novel syntheses of substituted pyrroles as key structural units of living matter (chlorophyll and hemoglobin), pharmaceuticals, and monomers for optoelectronic materials. It includes tables that provide references to original works, forming a guide to a variety of the reactions and synthesized compounds discussed. With coverage of the broad range of pyrrole chemistry and methods for their synthesis, it provides both a theoretical and an experimental basis for drug design.
The focus of this Thesis is on the synthesis and characterisation of aryloxides of the lanthanoid and alkaline earth metals with an emphasis on structural characterisation. One of the key objectives has been to explore the boundaries of the redox transmetallation/protolysis (RTP) reaction (formerly known as redox transmetallation/ligand exchange), and this is the focus of Chapter 2. Redox transmetallation/protolysis reactions were performed in the non-donor solvents toluene and hexane, in which success has not previously been achieved, and the reaction rates monitored by 19F NMR spectroscopy. A donor-solvent free pathway is proposed in which an intermediate of the type [Ln(C6F5)2(HOAr)n] is formed, and plays a pivotal role in determining the speed of the reaction. The application of this method for the synthesis of homoleptic products was established by the synthesis of the known homoleptic compounds [Ln(2,6-dpp)3] (Ln = La, Pr, Nd), [Ba2(2,6- dpp)4] (2,6-dppH = 2,6-diphenylphenol) and [La(2,6-dip)3]2 (2,6-dipH = 2,6- diisopropylphenol) as well as the isolation of new compounds [La4(3,5-dbp)12(3,5- dbpH)] and [Nd4(3,5-dbp)12(3,5-dbpH)]/[Nd4(3,5-dbp)10(3,5-dbpH)4(OH)2] (3,5- dbpH = 3,5-di-tert-butylphenol). A series of lanthanoid aryloxide complexes of the type [Ln(2,4-dbp)3(THF)3] (Ln = La, Pr, Nd, Gd, Er) were prepared by RTP reactions with 2,4-di-tert-butylphenol (2,4-dbpH) and structurally characterised (Chapter 3). Reaction in DME with neodymium afforded the seven-coordinate [Nd(2,4-dbp)3(DME)2], while the dinuclear [Yb2(2,4-dbp)6(DME)2] was obtained by an analogous reaction with ytterbium. Recrystallising the THF derivatives from toluene or hexane resulted in the loss of THF and the formation of the dinuclear [Ln2(2,4-dbp)6(THF)2] (Ln = Nd, Er). The structurally similar [Nd2(2,4-dbp)6(2,4-dbpH)2] was the product of a thermally induced protolysis reaction between the metal and the phenol. A RTP reaction between ytterbium metal and 2-tert-butylphenol (2-tbpH) did not give a solid product, however, the complex [Yb2(2-tbp)6(THF)2] was obtained after crystallisation from toluene. Extending this chemistry to the heavy alkaline earth metals, calcium, strontium and barium resulted in the isolation of a group of new and interesting compounds ii (Chapter 4). Reactions in THF afforded [Ca(2,4-dbp)2(THF)4] and [Sr3(2,4- dbp)6(THF)6], while analogous reactions in DME gave the remarkable [Ca2(2,4- dbp)4(DME)5], containing a bridging molecule of DME, and the asymmetrically bridged [Sr2(2,4-dbp)4(DME)3]. Reactions with the larger barium yielded cluster complexes [Ba8(2,4-dbp)12(OH)4(DME)4] and [Ba8(2,4-dbp)12(OH)4]. Chapter 5 details the synthesis and characterisation of a series of lanthanoid and alkaline earth calixarene complexes. Reactions between the lanthanoid metals and p- But-calix[4]arene in the presence of bis(pentafluorophenyl)mercury yielded [Ln(calix[4]OH)(THF)]2 complexes (Ln = Nd, Yb). Attempts to isolate divalent products through the strategic use of the p-But-calix[4](Et)2(OH)2 were unsuccessful, instead affording a series of chloride-containing complexes of the type [Ln(calix[4]Et2)Cl(THF)]2, in which the presence of the chloride arose from contamination of the starting material. A reaction between strontium metal and p- But-calix[4](OH)4 in the presence of bis(pentafluorophenyl)mercury afforded [Sr4(calix[4](OH)2)4(OH2)4(THF)4] after partial hydrolysis. A number of compounds prepared in the course of this work ([Nd(2,4- dbp)3(THF)3], [Gd(2,4-dbp)3(THF)3], [Ca2(2,4-dbp)4(DME)5], [Sr2(2,4- dbp)4(DME)3]) as well as the known compounds [Yb(ttfpz)2(THF)4], [Sm(dippForm)2(THF)2], [La(xylForm)3(THF)], [Sm(xylForm)3] and [Sm(mesForm)3] were taken to Oxford University and tested as potential initiators for the ring-opening polymerisation of rac-lactide. All were found to be capable of initiating polymerisation, albeit with varying degrees of success. Most systems could be improved by the introduction of a co-initiator (or chain-transfer agent) such as benzyl alcohol or benzylamine to promote immortal polymerisation. Chapter 6 provides detailed discussions of the polymer features, as well as kinetics studies of the rate of polymerisation in the cases of [Nd(2,4-dbp)3(THF)3], [Ca2(2,4- dbp)4(DME)5], [Sr2(2,4-dbp)4(DME)3] and [Sm(dippForm)2(THF)2] in the presence of benzylamine. Furthermore a structure-activity relationship for the alkaline earth initiators is discussed.
This dissertation describes the synthesis, characterization, and reactivity of organometallic complexes of yttrium and the lanthanides in an effort to more completely understand the nature of a recently-discovered class of +2 ions of these rare earth metals. The reactivity of complexes of a new set of Ln2+ ions (Ln = rare earth metal) with unprecedented 4fn5d1 electron configurations has been explored to expand the unique chemistry possible with the rare earth elements. The isolation of unexpected reaction products is described as well as the discovery of a new divalent lanthanide system and the utilization of solvent-free mechanochemical synthesis for established rare earth organometallic species. In Chapter 1, the reactivity of the highly-reducing, air-, moisture-, and temperature-sensitive divalent lanthanide complexes [K(2.2.2-cryptand)][Cp'3Ln] (Ln = Y, La, Ce, Dy) is characterized by examining reactions with aromatic organic substrates of known reduction potential. Complexes of the 4fn5d1 Ln2+ ions reduce naphthalene and biphenyl within minutes to form a new class of reduced aromatic complexes, [K(2.2.2-cryptand)][Cp'2Ln(n4-C10H8)] (Ln = Y, La, Ce, Dy) and [K(2.2.2-cryptand)][Cp'2Y(n6-C6H5Ph)], respectively. The naphthalene reactions also produced the previously unobserved ligand redistribution products [K(2.2.2-cryptand)][Cp'4Ln] (Ln = Y, La), which show the effect of the lanthanide contraction on structure as the lanthanum complex has four n5-Cp' rings while yttrium has three n5-Cp' rings and one n1-Cp' ring.
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