Multimetallic Alkaline-Earth Hydride Cations

Reactions of dimeric β-diketiminato (BDI) magnesium and calcium hydrides with [(BDI)Mg]+[Al{OC(CF3)3}4]- provide ionic multimetallic hydride derivatives, which have been characterized by single-crystal X-ray diffraction analysis. The exclusively magnesium centered species comprises a cation in which two [(BDI)Mg]+ units are connected by a single μ2-bridging hydride. In contrast, the greater lability of the calcium-containing system is underscored by the isolation of a cyclic heterotrimetallic species in which a CaH2 moiety is coordinated by a molecule of benzene and an aryl substituent of a [{(BDI)Mg}2H]+ cation. The homometallic dimagnesium species displays a greater facility toward reaction with diphenylacetylene than neutral [(BDI)MgH]2, although the resultant crystallographically characterized vinyldimagnesium cation equilibrates into a complex mixture of neutral and ionic species in solution. An initial assessment of both systems for the hydrosilylation of 1-hexene and diphenylacetylene evidences an inferior catalytic performance of [(BDI)MgH]2 in isolation.</p

Multimetallic Alkaline-Earth Hydride Cations

Reactions of dimeric β-diketiminato (BDI) magnesium and calcium hydrides with [(BDI)Mg]+[Al{OC(CF3)3}4]- provide ionic multimetallic hydride derivatives, which have been characterized by single-crystal X-ray diffraction analysis. The exclusively magnesium centered species comprises a cation in which two [(BDI)Mg]+ units are connected by a single μ2-bridging hydride. In contrast, the greater lability of the calcium-containing system is underscored by the isolation of a cyclic heterotrimetallic species in which a CaH2 moiety is coordinated by a molecule of benzene and an aryl substituent of a [{(BDI)Mg}2H]+ cation. The homometallic dimagnesium species displays a greater facility toward reaction with diphenylacetylene than neutral [(BDI)MgH]2, although the resultant crystallographically characterized vinyldimagnesium cation equilibrates into a complex mixture of neutral and ionic species in solution. An initial assessment of both systems for the hydrosilylation of 1-hexene and diphenylacetylene evidences an inferior catalytic performance of [(BDI)MgH]2 in isolation.</p

Allosteric control of supramolecular systems

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Alkaline-earth catalysts for biorenewable polymer synthesis

Plastics have become essential to 21st century human life; it is therefore unrealistic to reduce the usage of such single-life polymers enough to offset their hazardous environmental impacts. This has prompted research into the development of greener, non fossil-fuel based alternatives. Polylactide (PLA) is one such material; it is a biorenewable, biocompatible, aliphatic polyester that is most efficiently produced via the ring-opening polymerisation (ROP) of lactide (LA). The use of alkaline-earth metals, particularly the heavier congeners, in catalysts for this process has been understudied even though they offer advantages like high activity, low toxicity, low cost and lack of colour. The aims of this Thesis were therefore: (i) to prepare new alkaline-earth-based bimetallic, bis(phenoxy-imine) systems, (ii) to test their performance as initiators in LA ROP and (iii) to evaluate the benefits of bimetallic complexes/cooperativity for this type of polymerisation. The Thesis begins by offering a brief introduction to lactide as a biorenewable monomer in ring-opening polymerisation. The general ROP mechanisms are presented alongside a discussion of polymer characterisation techniques. An overview of previously reported catalysts for the ring-opening polymerisation of lactide is also described. A series of alkaline-earth complexes based on the “NOON” motif (H2DippL; 2,7-(HC=NDipp)-1,8-OH-C10H4) were synthesised and fully characterised. These compounds were applied towards the ROP of L-, D-, rac- and meso-LA; a variety of polymerisation conditions (temperature, monomer stereochemistry and initiator concentration) were studied to determine the kinetics, mechanism and overall rate equation of the polymerisation. It was found that all of the prepared initiators were active however, they either suffered from low activity (kobs = 0.0046–0.091 h–1 (Mg)) or poor polymerisation control (1.23 Related alkaline-earth “NON” (HR,DippL; 1-OH-2,6-(HC=NDipp)-4-R-C6H2 where R = H, Me, tBu) systems were then prepared and fully characterised in attempts to improve polymerisation control and activity. The homo vs. heteroleptic nature of these complexes was found to differ between metals as a result of varying steric shielding and bonding lability. In most cases, these monometallic species showed improved polymerisation activity (kp = 966 vs. 3.19 M–1 h–1 (Mg)) and control over their “NOON” counterparts. A variety of techniques were used to characterise the resultant polymers in order to deduce tacticity (Pr = 0.48-0.67), molecular weights and chain end groups. The “NON” framework was then explored, via several synthetic routes, for the formation of cationic, bimetallic alkaline-earth complexes. The generation of protonated proligands which could then be utilised for the insertion of multiple metals (Zn/Ca) by protonolysis was found to be a promising protocol

Developing anion recognition systems through hydrogen and halogen bonding interactions

Anions are ubiquitous in both environment and biological systems. Structurally complex anionic species, like DNA and RNA, are considered the blueprint of life. On the other hand, many simple anionic species play crucial roles in biological and ecological processes, such as iodide in hormone synthesis, fluoride in bone growth, and water pollution caused by per- and polyfluoroalkyl substances (PFAS). Given the above, there is a need to develop supramolecular anion recognition systems capable of binding various anionic species with distinct preferences and selectivity. In pursuit of this goal, my dissertation is focused on synthesizing new anion receptors through rational design and exploring their unique binding modes. By incorporating different noncovalent interactions, namely hydrogen bonding and halogen bonding, and different binding motifs in the host structure, some interesting anion recognition behavior has been achieved. Chapter 1 provides an introduction to the fundamentals of calix[4]pyrrole chemistry and an overview of recent progress in the area of bis-calix[4]pyrrole-based anion receptors. The underlying relationship between the number of so-called walls, structural rigidity and anion/ion pair selectivity is discussed and illustrated with examples. Chapter 2 describes a rationally designed “two wall” bis-calix[4]pyrrole anion receptor with a highly restricted inner cavity. This symmetric receptor was found capable of capturing fluoride anion with near-exclusive selectivity that proved to be dictated by its confined binding site as inferred from both experimental results and theoretical simulations. Chapter 3 details a halogen bonding based ditopic anion receptor inspired by the “Texas-sized” molecular box. An unconventional recognition sequence, which is exactly the reverse seen in traditional halogen bonding systems, was discovered. Additionally, enhancements in binding cooperativity directly related to the guest anion size were also observed. Chapter 4 introduces our ongoing effort to develop a halogen bonding based hyperbranched polymer. Taking advantage of both the hydrophobic nature of halogen bonding interactions and the abundant intramolecular cavities provided by hyperbranched polymeric networks, we postulate that it should be possible to create new materials that can extract PFAS pollutant from aqueous media with high affinity and capacity. Progress towards this latter goal is summarized.Chemistr

I. Discovery and development of nickel-catalyzed 1,2-dicarbofunctionalization reactions of alkenes II. Synthesis and reactivity of nucleophilic calcium fluoride complexes with oxygenic ligand frameworks

Part I. Discovery and Development of Nickel-Catalyzed 1,2-Dicarbofunctionalization Reactions of Alkenes. While much success has been achieved in the realm of 1,2-dicarbofunctionalization of alkenes under nickel catalysis, yet there remains a paucity in using weak directing groups, dicarbofunctionalizing multisubstituted alkenes, and implementing asymmetric variants. In our investigations, we developed a method where we can leverage weak ketone native directing groups for the 1,2-diarylation of unactivated alkenes with excellent regioselectivity. Additionally, we serendipitously discovered that sulfonamides are uniquely effective in directing 1,2- dicarbofunctionalization of unactivated alkenes including 1,2-disubstituted and trisubstituted alkenes. In light of these findings, we demonstrate an enantioselective variant which was plausible by tuning the steric bulk of the sulfonamide directing group and finding the adequate flexibility of a chiral N,N-ligand. Part II. Synthesis and Reactivity of Nucleophilic Calcium Fluoride Complexes with Oxygenic Ligand Frameworks. The inorganic salt CaF2 is insoluble in water and in organic solvents making it difficult to study in situ. While efforts have been made in the solid state, solution state investigations would greatly shed more light into the nature of the nucleophilicity of the Ca–F bond. The majority of the known soluble, well-defined, calcium fluoride complexes are typically stabilized by amido-type ligands, and with only one ligand archetype showing fluoride delivery capabilities. We sought to investigate O-donor ligand scaffolds that may also stabilize calcium fluoride complexes and improve fluoride anion delivery compared to the amido-supported counterpart. In our investigations, we found that the TACN ligand was appropriate owing to its macrocyclic design, which encapsulates calcium. However, a novel desymmetrizing method of a (TACN)Ca complex had to be developed which allowed leeway for the synthesis of various dinuclear calcium mono- and difluoride complexes. Fluoride anion delivery upon electrophiles was found to be enhanced when compared to the notorious NON ligand framework

Para-Functionalized NCN-Pincer Palladium and Platinum Complexes as Building Blocks in Organometallic Chemistry

A rapidly evolving field in chemistry is the application of organometallic and coordination complexes as building blocks or active components for the construction of new materials exhibiting specific catalytic, redox, optical or sensor activities. A central theme in the construction of these inorganic building blocks is the targeted functionalization of ligands, either prior to or, less conventionally, after the metallation step. Ligand functionalization enables the immobilization of the transition-metal complexes on macromolecular or inorganic supports, the regulation of their solubility, the introduction of additional functional moieties, as well as the electronic tuning of the metal. Furthermore, the functionalized complexes can be applied in inorganic crystal engineering or for targeted (supramolecular) assembly in solution. The NCN-pincer ligand (NCN = 2,6-bis[(dimethylamino)methyl]-phenyl anion) is a versatile building block for these purposes. NCN-pincer palladium(II) and platinum(II) complexes (Chart 1) are air- and water-stable, and find widespread applications in the field of catalysis and as sensor materials. Para-functionalization of these complexes offers an anchoring point, while leaving the structural integrity of the metal center intact. X M=Pd(II), Pt(II) ! X= counter ion and/or Me2N---M---Nme2 coordinating ligand ?? Z= functionalization site Z Chart 1 The results described in this thesis show that NCN-pincer palladium and platinum complexes are versatile building blocks for the construction of new organometallic materials with applications in diverse fields such as catalysis, crystal engineering, and (macro)molecular visualization. The pathways presented for the synthesis of the new para-functionalized NCN-pincer complexes are of crucial importance for generating a suitable anchoring point for further functionalizations without affecting the M C bond. Important aspects concerning their synthesis include: i) the exceptional stability of the NCN-complexes, allowing ligand modifications after the metallation step, and ii) the availability of various metallation procedures for selective introduction of the palladium or platinum center in the NCN-ligand. Both features offer a high degree of flexibility in the synthesis of the para-functionalized complexes, making functionalization with virtually any (organic) group feasible. Noteworthy are the linear Hammett correlations found for the para-substituted NCN-platinum complexes. Extension of these correlations to NCN-pincer complexes of other metals, and eventually to PCP- or SCS-pincer complexes, allows subtle tuning of the electron density on their metal centers, and consequently theoretical predictions of their catalytic and/or optical properties. The application of NCN-pincer building blocks in the examples shown in this thesis illustrate the above-mentioned features, i.e. selective metallation of the ligand at various stages of the syntheses and modifications on the ligand after the metallation step. The methodology employed in the preparation of the pincer complexes can be used as a starting point for the construction of new organometallic materials based on the pincer ligand. These materials can be designed to exhibit bio- or solvent-compatibility and/or specific aggregation behavior. Finally, (non)-covalent assembly of catalytically active NCN-pincer complexes with other functional moieties, e.g. (co)catalysts or receptor sites, offers the opportunity to construct bifunctional or supramolecular catalysts

Total synthesis of amaminol A

This thesis includes an extensive review of preparation of bicyclo[4.3.0]nonane derivatives. Bicyclo[4.3.0]nonanes can be prepared by several methods. The most important preparation method of bicyclo[4.3.0]nonanes is intramolecular Diels-Alder cycloaddition (IMDA). Several biologically active natural and unnatural compounds contain bicyclo[4.3.0]nonanes in their molecular framework. The synthetic efforts toward natural compounds such as pulo'upone, isopulo'upone, indanomycin, stawamycin, cochleamycin A, ikarugamycin and lepicidin A are surveyed in this thesis. The second part of the review includes preparation methods for bicyclo[4.3.0]nonane derivatives. The synthesis part of this thesis presents my own results of synthetic efforts on amaminol A. Amaminol A was obtained as the side product from the synthesis of amaminol A diastereomer. Although amaminol A was obtained as the side product, the developed route allows the preparation of amaminol A as the major product by changing the stereochemistry of the employed organocatalyst. The bicyclo[4.3.0]nonane part of amaminol A was obtained utilizing two different types of IMDA's. These were chiral auxiliary induced and organocatalytic IMDA cycloadditions. Many active organic molecules include vicinal amino alcohol moieties in their molecular framework. The preparation of vicinal amino alcohols from α-amino ketones was also studied in this thesis. Chelation type reduction was found to give the highest diastereoselectivities with N-tert-butylcarbamate protected α-amino ketone.reviewe

Тезисы докладов

В сборнике представлены тезисы докладов XXVI Международной Чугаевской конференции по координационной химии, VII Международного симпозиума “Дизайн и синтез супрамолекулярных архитектур” и III Молодёжной конференции-школы “Физико-химические методы в химии координационных соединений”, проходивших в Казани с 6 по 10 октября 2014 года.75