This thesis focuses on the design and development of novel versatile diamido ligands for transition metal and main group element chemistry. The central concept of this work deal relied on the design of N, N'-disubstituted-1,8-diaminonaphthalene (H2RR’-DAN) as proligands to dianionic diamido ligand scaffolds. These ligands would then be employed for stabilization of main group element (e.g. Li, B, Al) and transition metal (e.g. Ti, Zn) compounds.

京都大学 / 0048 / 新制・論文博士 / 博士(理学) / 乙第12840号 / 論理博第1542号 / 新制||理||1578(附属図書館) / 31423 / 京都大学大学院理学研究科化学専攻 / (主査)教授 大須賀 篤弘, 教授 丸岡 啓二, 教授 時任 宣博 / 学位規則第4条第2項該当 / Doctor of Science / Kyoto University / DGAM

Chalcogen bonding (ChB) is a particular case of secondary bonding centred on heavy group-16 elements. It is almost exclusively identified through crystallography by measuring interatomic distances intermediate between single-bond averages and the sum of van der Waals radii. However, there is significant recent progress in discerning its signatures using spectroscopic techniques such as multinuclear NMR. This M.Sc. thesis describes progress in two research projects on chalcogen bonding. The first examined the effect of halogenation on the aggregation of 3-methyl-5-phenyl 1-2-tellurazole 2-oxide. The second examined the strengthening of ChB interaction between molecules of benzo-1,2-chalcogenazole 2-oxides by chlorination. The bromination of 3-methyl-5-phenyl 1-2-tellurazole 2-oxide yielded 3,3,3-tri-bromo-3-methyl-5-phenyl-1,2-tellurazole-2-anole. Four unique crystal structures were obtained with the most promising being the dimeric structure. Deprotonation was unsuccessfully attempted although yielded 2 unique crystal structures co-crystallized with proton-sponge. Iodination of 3-methyl-5-phenyl 1-2-tellurazole 2-oxide was also performed, resulting in a mixed tetrameric aggregate containing two molecules of 3-methyl-5-phenyl 1-2-tellurazole 2-oxide and two 1,1-di-iodo-3-methyl-5-phenyl 1-2-tellurazole 2-oxide molecules. DFT investigations into the electronic properties, thermodynamics of aggregation, and basicity were performed. Similar to the chlorinated derivative, the most favourable aggregate to form is the hetero-tetramer with two brominated or iodinated molecules and 2 non-halogenated molecules. The reaction of benzo 1,2-sellenazole 2-oxide with SO2Cl2 and benzo 1,2-tellurazole 2-oxide with HCl followed by SO2Cl2 yielded halogenated derivatives of each molecule in which the chalcogen was oxidized from Ch(II) to Ch(IV). In the selenium derivative, an unexpected chlorination occurred on the heterocycle of the molecule. Crystal structures were obtained for each chlorinated product where dimeric interactions were observed. DFT calculations show how the electronic and orbital mixing contributions to the ChB interactions are enhanced upon halogenation. Gibbs free energy of aggregation is most negative for a mixed structure in which two chlorinated molecules and two unchlorinated molecules are linked. / Thesis / Master of Science (MSc)

This thesis describes selected reactivity studies of group 15 Zintl anion [E7]3– (E = P, As) derived cages towards a series of unsaturated organic molecules. The synthesis and characterization of forty-two compounds derived from [E7]3– cages are detailed herein. A high yielding procedure for the synthesis of [HE7]2– (E = P, As) from the K3E7 Zintl phase has been developed. This solves prior issues with poor solubility and variable purity of the Zintl phases. The conditions required for the deprotonation of the phosphorus congener to [P7]3– are described. The reactivity of both [P7]3– and [HP7]2– towards carbon dioxide and isolobal isocyanates and carbodiimides was explored. This yielded a series of monofunctionalized [E7R]2– cages, via a net hydropnictination of a C=N double bond of the organic substrate. The protonation chemistry of these anions was further investigated, resulting in the formation of the protic [HP7C(NHDipp)(NDipp)]– cluster. This anion is capable of further hydrophosphination chemistry to give a series of difunctionalized heptaphosphide cages. The reaction of [E7]3– with alkynes results in the formation of the relatively unusual 1,2,3-tripnictolide anions. A series of such anions have been prepared, encompassing all of the previously reported anions and several novel species. Investigation of the coordination properties of these cyclopentadienyl analogues shows that they are superior π acceptor ligands. A synthetic route to [P5]– as a compositionally pure solid, and some initial studies on its protonation chemistry are also additionally presented.

The synthesis and reactivity of a number of mixed transition metal-aluminium and σ-alane complexes are detailed in this thesis. Chapter III reports on the formation and structural characterisation of N,N'-chelated aluminium dihalide precursors featuring amidinate and guanidinate substituents. These precursors of the type RC(R'N)₂AlX₂ (R = ⁱPr₂N or Ph; R' = Cy or ⁱPr or Dipp; X = hal), readily react with Na[CpFe(CO)₂] via salt elimination to form the corresponding mixed iron-aluminium complexes CpFe(CO)2[(X)Al(NR')2CR] which have been characterised both spectroscopically and by X-ray diffraction. The reactivity of the novel mixed aluminium-iron complexes towards halide abstraction agents has been investigated and a propensity for augmented coordination at the aluminium centre observed. Furthermore, complementary syntheses of the methyl substituted complex CpFe(CO)₂[(Me)Al(NCy)₂CNⁱPr₂] have been developed. This can be achieved either via the reaction between the related chloride complex and MeLi, or from the reaction between ⁱPr₂C(CyN)₂Al(Me)Cl and Na[CpFe(CO)₂]. The research detailed in Chapter IV builds on the previous chapter and is focussed on the use of more sterically demanding substituents at both aluminium and transition metal, as well as more electron rich transition metal fragments. The transition metal anions Na[Cp*Fe(CO)₂] and Na[Cp^SiFe(CO)(PPh₃)] react with the aluminium precursors forming related mixed iron-aluminium complexes which have been structurally characterised. The Dipp₂NacNacAlCl₂ precursor has been shown to undergo reaction with both Na[CpFe(CO)₂] and Na[Cp*Fe(CO)₂]. The halide abstraction chemistry of the latter utilising both Lewis acid and salt metathesis based abstraction approaches has been investigated. The dehydrohalogenation chemistry of the Dipp₂NacNacAlCl₂ precursor was investigated and the ligand activated products of reactions with both alkyl lithium and alkyl potassium reagents characterised. Chapter V reports the extension of salt metathesis for the formation of an Al-H-Mn interaction, and the product has been fully characterised. In addition, the coordination of Al-H bonds from a number of alane precursors to in situ generated 16-electron fragments has allowed the structural characterisation of a number of novel σ-alane complexes. The incorporation of the transition metal fragments [Cp'Mn(CO)₂] and [W(CO)₅] permit comparison to archetypal borane and silane σ-complexes. Quantum chemical calculations suggest that the alane ligand has a binding energy close to that of dihydrogen but significantly less than that of CO, consistent with a predominant σ-donor role of the Al-H bond. The formation and structural characterisation of the κ²-complexes (OC)₄M[κ²-H₂AlDipp₂NacNac] (M = Cr, Mo or W) define an unprecedented binding motif for the alane ligand. In the cases of chromium and molybdenum the κ²-complexes can be prepared either photolytically or via alkene displacement from the corresponding (OC)₄M(cod) reagent. In the case of tungsten the alkene displacement route yields the desired product, but only under more forcing conditions. Spectroscopic characterisation of the related κ¹-complex (OC)₅Cr[κ¹-H₂AlDipp₂NacNac], which readily forms the κ²-complex in solution without photolysis, has enabled the kinetics of chelate ring closure to be investigated. This analysis further characterises the formation of the unprecedented κ²-binding motif for the alane ligand.

This work was initially launched to study the synthesis of low-valent group 13 compounds bearing the bis(imino)pyridine ligand framework. Since its inception, this project has grown beyond the boundaries of group 13 to include low valent tin, silver, and rhenium. Alongside the reports of novel coordination compounds, we utilized computational chemistry to uncover unprecedented interactions which challenge conventional concepts of bonding. Synthesis, characterization, and complimentary computational studies are presented herein. Chapter 1 presents a historical overview of the bis(imino)pyridine ligand as well as our synthetic methodology and characterization of new ligand variants we have contributed to the literature. Chapter 2 presents the synthesis of a series of In(I) and In(III) bis(imino)pyridine complexes with varied sterics. Ligand-metal interaction and effect of ligand steric bulk on complex stability, as well as computational studies highlighting weak covalent interactions will be discussed. Chapter 3 presents the synthesis of Ga(III) bis(imino)pyridine complexes. Reactivity with “GaI” synthon as well as varied-stoichiometry one-pot synthesis attempts to generate low valent Ga-bis(imino)pyridine complexes will be discussed. Chapter 4 presents the synthesis of a series of Tl(I) bis(imino)pyridine complexes with varied sterics analogous to the approach taken with indium(I). Unprecedented weak ligand-metal as well as Tl-arene interactions will be discussed. Chapter 5 presents the synthesis of a series of Sn(II) bis(imino)pyridine complexes with varied sterics and halide substituents. Preferential cation-anion pair formation and attempted reactivity will be discussed. Chapter 6 presents the synthesis of a series of Ag(I) bis(imino)pyridine complexes with varied sterics. Resulting ligand-metal interactions as well as reactivity towards Lewis basic donor ligands will be discussed. Chapter 7 presents the synthesis of first crystallographically authenticated examples of rhenium(I) pincer complexes utilizing the bis(imino)pyridine ligand. Chapter 8 presents a general conclusion to the work.

Only within the last decade has supramolecular chemistry begun to adopt the Group 15 elements into its field of research. This dissertation presents a supramolecular approach to the self-assembly and reactivity of Group 15 metalloids, specifically arsenic and antimony, with organothiolate ligands. Investigating the self-assembly of pnictogen-based coordination complexes allows for in-depth characterization of the chemical behavior of arsenic, antimony and other Group 15 elements. Currently, the infiltration of arsenic into global groundwater systems has developed into a worldwide health concern. There are no chelating agents available for public use in the treatment of arsenic poisoning which are capable of binding arsenic (III) in its preferred coordination geometry thereby hindering the selectivity for rapid chelation. Chapter I is a review covering two important characteristics observed in the Group 15 elements: 1) a stabilizing, non-covalent cation-π interaction aiding in the formation of pnictogen-aryl thiolates, and 2) an observed lack of selectivity in environments containing multiple pnictogen ions which enables transmetalation of the complexes to occur or the generation of heterometallic assemblies. Based on the discovery of this new transmetalation reactivity, the remainder of the dissertation explores the effects of external additives during self-assembly in order to understand how they may affect the reactivity of these self-assembled complexes and provide insight into formation mechanisms. Chapter II identifies a catalyst for the acceleration of a slow self-assembly reaction between AsCl3 and a dithiolate ligand to give an As2L3 cryptand. Chapter III examines the oxidation of the arsenic cryptand using iodine, which leads to the self-assembly of a series of differently sized, discrete disulfide-bridged macrocycles. In Chapter IV, the self-assembly of the first trinuclear arsenic- and antimony-based coordination complexes was studied, revealing interesting solvent dependent conformational isomerism in solution. Chapter V applies the pnictogen-enhanced iodine oxidation to the synthesis of known and new cyclophanes using supramolecular chemistry, including the self-assembly and covalent capture of an unprecedented tetrahedral thiacyclophane. Additionally, an unusual trithioorthoformate capped tricyclophane cage was also synthesized and isolated by pnictogen-activated oxidation. Chapter VI includes the conclusion and future directions for the project. This dissertation includes co-authored material and previously published results. / 10000-01-01

The most efficient homogeneous catalysts for hydroxylation of light alkanes utilize transition metals in superacid solvent and operate by tandem electrophilic C-H activation/metal-alkyl (M-R) functionalization. An emerging alternative strategy to transition metals is the use of high-oxidation state main-group metals (e.g. TlIII, PbIV, IIII) that hydroxylate light alkanes. This dissertation reports density-functional theory calculations that reveal the mechanisms, reactivity, and selectivity of TlIII promoted alkane C-H functionalization in trifluoroacetic acid and TlIII-dialkyl functionalization in water. Calculations reveal that TlIII oxidizes alkanes via a closed-shell C-H activation and M-R functionalization mechanism that is similar to transition-metal C-H functionalization mechanisms. Comparison of TlIII to similar transition metals reveals that while TlIII and transition metals can have similar activation barriers for C-H activation, TlIII M-R functionalization is significantly faster due to a highly polar Tl-C bond and large TlIII/TlI reduction potential. The combination of a moderate C-H activation barrier combined with a low M-R functionalization barrier is critical to the success for TlIII promoted alkane C-H oxidation. The proposed TlIII C-H activation/M-R functionalization mechanism also provides an explanation for ethane conversion to a mixture of ethyl trifluoroacetate and ethane-1,2-diyl bis(2,2,2-trifluoroacetate). The reactivity of TlIII contrasts the lack of alkane oxidation by HgII. The C-H activation transition state and frontier-orbital interactions provide a straightforward explanation for the higher reactivity of TlIII versus HgII. This frontier-orbital model also provides a rationale for why the electron-withdrawing group in EtTFA provides "protection" against overoxidation. Calculations also reveal that TlIII-dialkyl functionalization by inorganic TlIII in water occurs by alkyl group transfer to form a TlIII-monoalkyl complex that is rapidly functionalized.

The recognition and capture of fluoride, cyanide and azide anions is attracting great deal of attention due to the negative effects of these anions on the environment and on human health. One of common methods used for the recognition and capture of these anions is based on triarylboranes, the Lewis acidity of which can be enhanced via variation the steric and electronic properties of the boron substituents. This dissertation is dedicated to the synthesis of novel boron-based anion receptors that, for the most part, feature an onium group bound to one of the aryl substituents. The presence of this group is shown to increase the anion affinity of the boron center via Coulombic effects. Another interesting effect is observed when the onium group is juxtaposed with the boron atom. This is for example the case of naphthalene-based compounds bearing a dimesitylboryl moiety at one of the peri-position and a sulfonium or telluronium unit at the other peri position. Fluoride anion complexation studies with these sulfonium or telluronium boranes, show that the boron-bound fluoride anion is further stabilized by formation of a B-F->Te/S bridge involving a lp(F)->sigma*(Te/S-C) donor acceptor interaction. Some of the sulfonium boranes investigated have been shown to efficiently capture fluoride anions from wet methanolic solutions. The resulting fluoride/sulfonium borane adducts can be triggered to release a "naked" fluoride equivalent in organic solution and thus show promise as new reagents for nucleophilic fluorination chemistry. Interestingly, the telluronium systems show a greater fluoride anion affinity than their sulfonium analogs. This increase is assigned to the greater spatial and energetic accessibility of the sigma* orbital on the tellurium atom which favors the formation of a strong B-F->Te interaction. This dissertation is concluded by an investigation of the Lewis acidic properties of B(C6Cl5)3. This borane, which has been reported to be non-Lewis acidic by other researchers, is found by us to bind fluoride, azide and cyanide anions in dichloromethane with large binding constants. This borane is also reactive toward neutral Lewis bases, such as p-dimethylaminopyridine, in organic solvents.

This work was initially launched to study the synthesis of low-valent group 13 compounds bearing the bis(imino)pyridine ligand framework. Since its inception, this project has grown beyond the boundaries of group 13 to include low valent tin, silver, and rhenium. Alongside the reports of novel coordination compounds, we utilized computational chemistry to uncover unprecedented interactions which challenge conventional concepts of bonding. Synthesis, characterization, and complimentary computational studies are presented herein. Chapter 1 presents a historical overview of the bis(imino)pyridine ligand as well as our synthetic methodology and characterization of new ligand variants we have contributed to the literature. Chapter 2 presents the synthesis of a series of In(I) and In(III) bis(imino)pyridine complexes with varied sterics. Ligand-metal interaction and effect of ligand steric bulk on complex stability, as well as computational studies highlighting weak covalent interactions will be discussed. Chapter 3 presents the synthesis of Ga(III) bis(imino)pyridine complexes. Reactivity with “GaI” synthon as well as varied-stoichiometry one-pot synthesis attempts to generate low valent Ga-bis(imino)pyridine complexes will be discussed. Chapter 4 presents the synthesis of a series of Tl(I) bis(imino)pyridine complexes with varied sterics analogous to the approach taken with indium(I). Unprecedented weak ligand-metal as well as Tl-arene interactions will be discussed. Chapter 5 presents the synthesis of a series of Sn(II) bis(imino)pyridine complexes with varied sterics and halide substituents. Preferential cation-anion pair formation and attempted reactivity will be discussed. Chapter 6 presents the synthesis of a series of Ag(I) bis(imino)pyridine complexes with varied sterics. Resulting ligand-metal interactions as well as reactivity towards Lewis basic donor ligands will be discussed. Chapter 7 presents the synthesis of first crystallographically authenticated examples of rhenium(I) pincer complexes utilizing the bis(imino)pyridine ligand. Chapter 8 presents a general conclusion to the work.