Academic literature on the topic 'Organocobalt compounds'

This thesis reflects two main aims. Firstly, the synthesis and characterisation of a number of potential anion receptors was undertaken and their anion binding properties were assessed. In so doing, a second aim was fulfilled, namely a comparison of the various methods of detecting the bound anion, and quantifying the binding strength. Four techniques appear in this thesis; ¹H nuclear magnetic resonance, UV-visible spectroscopy, electrochemistry and luminescent emission. Quantitative titrations were performed and, where possible, stability constants estimated. Chapter One provides an introduction to some of the themes of molecular recognition and provides a brief overview of the literature associated with anion recognition. A Prologue describes the design of the receptors studied; they all incorporate a metal centre and appended amide groups which provide sources of hydrogen bonding. The molecules are mostly cationic and a combination of positive charge and hydrogen bonding constitutes the binding interaction. Chapter Two is concerned with receptors based on cobalticinium, [Cp₂Co] ⁺ . A number of receptors are presented and are found to bind anions with stability constants typically in the range of 500-1000 dm³mol^-1 . Receptors involving more than one cobalticinium centre are found to bind much more strongly and, furthermore, variations in functional groups appended close to the proposed coordination site impart selectivity; dihydrogen phosphate is bound more strongly than chloride. It is also found that different techniques give different stability constants and comment is made on this phenomenon. Chapter Three examines the role of positive charge in anion binding and describes the synthesis and coordination properties of several neutral receptors. These molecules retain hydrogen bonding sites, and it is found that this is sufficient to bind anions, but the strength of the interaction is greatly reduced. Chapter Four introduces another system, based on RuL(bpy)₂²⁺ , where L is a 4,4'-amide disubstituted bpy. The strength of binding is an order of magnitude greater than the cobalticinium systems as detected by several methods including emission studies, which are very sensitive. Comparison with a neutral, rhenium-based receptor is made. A dihydrogen phosphate-selective luminescent sensor is also presented. The Epilogue identifies areas for future research. Specialised introductions and summaries are found at the beginning and end of each chapter.

A series of 2,6- and 3,5-ethynylpyridyl compounds and their cobalt clusters have been prepared and analysed in Chapter 2, in order to study through-space and through-bond interactions between the ethynyl arms. Bidentate N- donor ligands, such as bipyridine and o-phenanthroline with alkyne functionality have been used extensively as building blocks for a wide range of molecular materials, but monodentate ethynylpyridyls have received less attention. The results showed that while there is no orbital restriction on a RC[triple bond]C-n-[pi]�cc-C[triple bond]CR through-bond interaction in 2,6-ethynylpyridyls, no significant interaction exists. Nevertheless, there are intramolecular interactions as manifested in the distortions which occur in the solid state structure of the compounds and the lability of the diphenylphosphine methane (dppm) moieties in the oxidised Co₂(CO)₄dppm species. Polymerisation by Sonogashira coupling between dibromo pyridines or diiodo ferrocene and ethynyl pyridines resulted in only oligomeric fractions that could be separated. The thesis also reports the synthesis and characterization of some novel naphthalimide monomers with acrylic and allyl headgroups. The naphthalimide moiety is substituted in the 4-position with various functionalities. This is presented in detail in Chapter 3 of the thesis. The monomers� structure is the following: [illustration omitted] wherein: A may be a polymerizable group (methacrylate or allyl), which includes a spacer entity (aliphatic or aromatic); B is selected from an ethenyl or ethynyl linked organometallic group, a halogen and/or an amine (i.e. bromo, ethynylferrocene, ethenylferrocene, trimethylsilylethynyl, nitro, piperidine and ethenylpiperidine). The acrylic monomers were synthesized by coupling 4-bromo-1,8-naphthalic anhydride with an amino alcohol to give an imide, which then was coupled with methacryloyl chloride to provide the methacrylate. Functionalization in the 4-position of the naphthalimide moieties was achieved by Sonogashira and Heck coupling reactions with for example ethynylferrocene, trimethylsilyl acetylene, vinylferrocene. For the allyl monomers synthesis, a reaction between allyl amine and 4-Bromo-naphthalic anhydride provided 4-bromo-naphthalimido allyl, which was then functionalized by further Sonogashira and Heck coupling reactions. The monomers were polymerised and copolymerised with other widely used comonomers, such as methyl methacrylate, methyl acrylate, styrene, vinyl carbazole and acrylonitrile. The polymerisation processes and the full analyses of the (co)polymers are described in Chapter 4. Free radical polymerisation, FRP, initiated by azo bisisobutyronitrile, AIBN at elevated temperature was the main technique employed for making the (co)polymers. Atom Transfer Radical Polymerisation, ATRP was conducted for some monomers although the results were inconclusive (the yields were low, under 50%, but the molecular weight distributions were quite narrow, PDI�s <1.7). Heck coupling polymerisation was performed for the bromo- substituted methacrylic and allyl monomers and supplied colorful, well-defined polymeric materials, with low polymerisation degrees. All polymers were analyzed by HPLC, NMR, UV-VIS, IR, electrochemistry and fluorescence. The (co)polymers made by FRP had various molecular masses (Mn = 3000- 90.000), whereas the polydispersities were PDI = 1.4- 4.6. Most of the (co)polymers were fluorescent and had good thermal and electrochemical properties. Potential applications of the polymers have been suggested and relevant literature background in the field is provided in both Chapters 1 and 4. The monomers/ polymers are stable compounds (no special storage conditions required) and can act as good candidates for potential applications in light emitting devices, as resins/ binders for coating materials, in the dyes and pigment industry and also for manufacturing of conducting polymers and/or composite materials.

This programme of work has focused at developing novel cyclisation reactions in order to furnish a variety of carbocyclic ring systems. The formation of these ring systems have all been based around a key cyclisation step, which has involved a novel ‘intra’molecular Nicholas reaction. The use of organcobalt clusters for our work is based around the Nicholas reaction which is the reaction of cobalt complexed propargyl alcohol/ethers with a Lewis acid. This provides an ‘in situ’ cobalt stabilised carbocation that can be reacted with a range of nucleophiles to provide alkylated products. The first chapter reviews tandem cyclisation reactions and their role in organic chemistry. This is followed by a review of the chemistry of organocobalt clusters and the following chapter reports the results of our investigations. The initial investigation followed existing studies, carried out at Kingston University, in an attempted synthesis of bicycle(4:4:0)decanes. These fused carbocycles represent the AB ring system of the steroid nucleus. This work focused upon an investigation into the oxidation of propargyl alcohols to form propargyl aldehydes, using a variety of mild oxidation methods. The cobalt complex of propargyl aldehyde is synthetically useful as it is able to undergo a Nicholas reaction to afford the corresponding propargyl alcohol thus enabling a further Nicholas reaction to be performed. This work was successful in synthesising a cyclisation precursor that contains two centres. When complexed with dicobalt hexacarbonyl it has been possible to separate the diastereomers formed and determine their relative stereochemistry using [sup]1H NMR techniques. These studies then progressed and a novel tandem cyclisation reaction was discovered that provided tricyclic compounds from a monocyclic precursor. The tandem sequence appears to take place ‘via’ an ‘inter’molecular Nicholas reaction followed by an ‘intra’molecular Nicholas reaction. During the sequential decomplexation step of the dicobalt hexacarbonyl complex, an additional cyclisation occurs to afford tricyclic compounds with a further functional group interconversion. For example, applying this one pot synthesis to 3-(4-methyl-3-pentenyl)-1-(trimethyl silyloxy)-1-cyclohex-1-ene, the synthesis of 6,6-dimethyltricyclo(7:4:0:0[sup] 3,7)tridec-4-en-1-one was achieved. It was discovered that some of the cyclisation precursors used, underwent the tandem Nicholas reactions to produce a bicyclic compound, but failed to undergo the additional cyclisation to produce the corresponding tricyclic compounds. For example by applying the methodology to carvone the resulting compound obtained was 3-ethynyl-2-methyl-4-(1-methyl-1-ethenyl)-9-(1-methyl-1-ethenyl)bicyclo(4:4:0)decan-1-one. The final section concludes these investigations by describing the experimental procedures for all the reactions performed.

CoN₆ amine systems have played important roles in chemistry since the early days of the coordination chemistry. And the prospect for synthetic development and interesting properties of such molecules continues to stimulate efforts to advance its chemistry. Exploration of some recent new advances in this area dominates this thesis in which the synthesis, chemical and physical properties and biological activities of several new molecules are described. In the first Section, Chapter One outlines the history of CoN₆ amine systems and describes some interesting developments and prospects arising from these systems. Chapter Two describes the general experimental details including syntheses and procedures, but the syntheses relating to new strategies are given in the appropriate individual chapters. The second Section, containing Chapters Three and Four, describes the syntheses, structures and properties of coordinated methanimines which are believed to be important intermediates in the syntheses of hexaamine cage complexes. It is found that the normally extremely unstable organic poly-methanimines are stabilised by coordination, and that the coordinated methanimine complexes are sufficiently stable to use as synthetic reagents. The single crystal X-ray analyses of three poly-methanimine complexes, [Co(CH₂)₃-sen]³⁺ and [Co((CH₂h₂-en)₃]³⁺ and [Co((CH₂)₃-tame₂)J³⁺, show the structures of the methanimine moieties which would be very difficult to synthesize and maintain in the absence of the metal. These studies of coordinated methanimines open up new versatile ways to generate 3-dimensional polyamine assemblies not only more efficiently but also more selectively. The mechanisms for template encapsulation syntheses are also more clearly understood from the studies involving intermediate mono and poly-methanimine molecules and other isolated products. Chapters Five and Six in Section Three deal with cobalt Meg-tricosaneN6 expanded cage systems. Both Co(II) and Co(Ill) complexes have been isolated and their properties studied. The Co(II) system displays an unique stability against oxidation by 02 in both solution and solid states. X-ray analyses and NMR studies indicate that both conformational and asymmetric nitrogen configuration changes occur relatively easily for the Co(II) complexes. One isomer of the Co(III) cage is fairly stable even though it is shown to be an efficient oxidant. Different Co(III) isomers have been isolated in the solid state. One form has an extraordinary blue colour and another is orange. The solid ⁵⁹Co MAS NMR spectrum shows a very large downfield chemical shift (ca 4000 ppm) from the orange to the blue form. The reflectance spectra imply a very weak ligand field at the cobalt site of the blue form. Another major factor is that the redox potential can be changed by at least 0. 7 V with the same metal ion couple and the same set of ligating atoms merely by influencing the steric factors in the cage. Paramagnetic cobalt (III) isomers have also been in evidence, but only investigated in preliminary ways in this work. The Me₈-tricosaneN₆ bicyclic cage free ligand is isolated by a relatively simple one-pot method. The synthesis of this sterically crowded extended cavity cage ligand also leads to possibilities for encapsulating and stabilizing larger metalions which do not fit readily in the smaller sar type ligand cavities. For example, the larger Cu(I) ion is tolerated in the octa methyl cage ligand, as demonstrated by the chemically reversible cyclic voltammetry of the [Cu(Me₈-tricosaneN₆)]²⁺/¹⁺ couple and the details are discussed in Chapter Seven. In the fourth Section, Chapter Eight describes the syntheses of polymeric cage complexes. The trimeric cage complex inherits many properties from the parental monomeric cages as well as showing electrostatic coupling between CoN6 moieties. It also demonstrates the potential for these molecules to be used as multiple electron transfer agents. The dimer cage [Co(CH₃,CH₂)sar-Co(NH,NH₂)sar]⁶⁺ and trimer cage [Co(CH₃,CH₂)sar-Co(NH,NH)sar-Co(CH₂,CH₃)sar]⁹⁺ compounds are further invested by reaction with DNA, the results implying that they interact with DNA chiefly by electrostatic binding. They are also found to photochemically cleave DNA by a mechanism which involves LMCT and the formation of a ligand radical oxidant. Chapter Nine in Section Four presents syntheses and properties of highly charged surfactants. These molecules show typical detergent properties and also demonstrate biological activity as in vitro anthelmintic agents. Some of the results obtained in this thesis do not seem to have any precedent in MN 6 chemistry and are related to fundamental changes in the nature of the MN 6 structure. Therefore they are not all well understood at this point. They all demonstrate, however, the versatility of MN6 systems and further work based on the studies in this thesis may help to advance important new insights into coordination chemistry. Some results, such as the coordinated methanimine compounds, are believed to be not only useful for inorganic synthesis but also for organic chemistry.