No description available.

No description available.

M.Sc. / Please refer to full text to view abstract

The work described in this thesis is in two essentially independent parts. In Chapter 3, we have studied the infrared spectra of the alkaline earth and first-row transition metal bisfluorosulfates over the frequency range 4000 – 250 cm⁻¹ in an attempt to resolve discrepancies in the literature on the infrared spectra of these compounds. We have obtained spectra for these compounds which are easily assigned and we suggest that the discrepancies in the literature may be due to differences in crystalline modifications studied by the different workers. We have also checked the reliability of infrared frequency shifts as measures of cation-anion interaction in fluorosulfate compounds. We observe a general increase in frequencies for the symmetric SO₃ stretching and S-F stretching modes with increasing interaction, but no quantitative relationship is present. However, the S-F stretching mode is shown to give a good indication of cation-anion interaction for compounds with predominantly ionic character. In the second part of this thesis, described in Chapter 4, we have prepared tetrakis(pyridine) complexes of nickel(II), copper(II) and zinc(II) fluorosulfates. In order to determine the coordination strength of the fluorosulfate ion relative to other ions, we have also prepared and characterized complexes of the general formula Cu(py) ₄X₂ (X = C10₄ˉ, BF₄ˉ, N0₃ˉ, CH₃C₆H₄SO₃ˉ, CF₃COOˉ ) by infrared, electronic, and electron paramagnetic resonance spectroscopy, electrical conductivity, and magnetic susceptibility measurements. The results indicate that on the whole, the coordination strength of SO₃Fˉ towards metals is similar, but slightly stronger than CIO₄ˉ and BF₄ˉ , definitely stronger than PF₆ˉ, and weaker than ReO₄,ˉ, CH₃C₆H₄SO₃ˉ and CF₃C00ˉ . / Science, Faculty of / Chemistry, Department of / Graduate

An understanding of the electrochemical properties of organometallic nitrosyl compounds provides a good understanding of their chemistry and a more rational way to approach synthetic investigations. Cyclic voltammetry studies of [(ƞ)⁵-C₅H₅)Cr(NO)₂]₂ in CH₂Cl₂ and CH₃CN reveal that the dimer undergoes a single two-electron oxidation to form [(ƞ⁵⁻C₅H₅)Cr(NO)₂]⁺ which is reduced to [(ƞ⁵-C₅H₅)Cr(NO)₂]• (or [(ƞ⁵-C₅H₅)Cr(NO)₂(CH₃CN)]• in the presence of CH₃CN) in a subsequent reduction step. The radical couples to form [(ƞ⁵-C₅H₅)Cr(NO)₂]₂ or decomposes. The dimer also is reversibly reduced in a one-electron step in CH₂Cl₂ and quasi-reversibly in CH₃CN. These inferences are supported by cyclic voltammograms of (ƞ)⁵-CH₅)Cr(NO)₂BF₄ and [(ƞ⁵-C₅H₅)Cr(NO)₂(CH₃CN)]PF₆. In contrast, the isoelectronic dimer [(ƞ⁵-C₅H₅)Fe(CO)₂]₂ oxidizes in two one-electron steps (the first of which is reversible and negative of the oxidation of [(ƞ⁵-C₅H₅)Cr(NO)₂]₂) and reduces to form [(ƞ⁵-C₅H₅)Fe(CO)₂]⁻. The differing oxidation behaviours of these dimers suggest that their reactions with HBF₄•OMe₂ [(ƞ⁵-C₅H₅)Cr(NO)₂]₂ cleaves into [(ƞ⁵-C₅H₅)Cr(NO)₂]⁺ and [ƞ⁵-C₅H₅)Fe(CO)₂]₂ forms [ {(ƞ⁵-C₅H₅)Fe(CO)₂}₂H]⁺) do not occur by initial electron transfer. The new radical anion complex [(ƞ⁵-C₅H₅)Fe(ƞ⁶-C₆Me₆)] [ {(ƞ₅-C₅H₅)Cr(NO)₂}₂] can be isolated by reaction of the neutral dimer with (ƞ⁵-C₅H₅)Fe(ƞ⁶-C₆Me₆) in Et₂0. Its spectroscopic properties are consistent with derealization of the extra electron onto the NO ligands, particularly the bridging nitrosyl groups. These observations provide a better understanding of the reactivity of [(ƞ⁵-C₅H₅)Cr(NO)₂]₂ with- nucleophiles. A comparative electrochemical study of the oxidations of [(ƞ⁵-C₅H₅)M(NO)₂R (M = Cr, R = CH₃; M = Mo, W, R = CH₃, C₂H₅),(ƞ⁵-C₅H₅)Fe(CO)₂CH₃ and (ƞ⁵-C₅H₅)M(CO) ₃R (M = Cr, R = CH₃; M = Mo, W, R = CH₃, C₂H₅) in CH₂Cl₂ reveals that the dinitrosyl complexes are harder to oxidize than their related carbonyl compounds. Electrophilic cleavage reactions of M-R bonds in these complexes, which proceed differently for the nitrosyl and carbonyl complexes are proposed to involve different mechanisms, with the nitrosyl-alkyl complexes reacting with electrophiles by direct attack at the metal-alkyl bonds, rather than by prior oxidation. Interestingly, (ƞ⁵-C₅H₅)Cr(NO) ₂CH₃ reacts with NOPF₆ to form the NO-insertion product [(ƞ⁵-C₅H₅)Cr(NO)₂(CH₂NOH)]PF₆ which has been structurally and spectroscopically characterized. The reactions of (ƞ⁵-C₅H₅)M(NO)₂CH₃ (M = Mo, W) with electrophiles and oxidants result in cleavage of the M-CH₃ bonds. The complexes (ƞ⁵-C₅H₅)M(NO)₂Y (M = Cr, Y = CH₃; M = Mo, Y = CH₃, C₂H₅, Cl; M = W, Y = CH₃, C₂H₅, H, Cl), [(ƞ⁵-C₅H₅)M(NO)₂L] BF₄ (M = Mo, L = PPh₃; M = W, L = PPh₃, P(OMe)₃, ƞ²-C₈H₁₄) and W(NO)₂Cl₂L₂ (L = P(OMe)₃, PMePh₂) exhibit quite reversible, one-electron reductions in CH₂Cl₂ and the new radical complexes [(ƞ⁵-C₅H₅) ₂Co] [(ƞ⁵-C₅H₅)M(NO)₂Y] (M = Mo, Y = CH₃, C₂H₅, Cl; M = W, Y = CH₃, H, Cl) are isolable by reactions of (ƞ⁵-C₅H₅)₂Co with the neutral precursor. Spectroscopic characterization of these and an X-ray crystallogrpahic analysis of [(ƞ⁵-C₅H₅)₂Co] [(ƞ⁵-C₅H₅)Mo(NO)₂C₂H₅] suggest that the anions possess monomeric, "three-legged piano stool" geometries with delocalization of the extra electron onto the NO ligands. In light of these observations the chemistry of (ƞ⁵-C₅H₅)M(N0)₂Y complexes becomes more understandable. / Science, Faculty of / Chemistry, Department of / Graduate

The reaction of chromocene with nitrogen monoxide in a variety of organic solvents leads to the formation of CpCr(NO)₂ (n¹-C₅H₅) as the major product, as well as CpCr(NO)₂ (NO₂) and [CpCr(NO)₂]₂ as minor products. Their formation in these conversions can be rationalized in terms of the reactive intermediate CpCr(NO) ₂. The reaction of photochemically generated molybdenocene with nitrogen monoxide to produce CpMo (NO) ₂ (n¹-C₅H₅) is also described. Sodium dihydridobis(2-methoxyethoxy)aluminate, I, undergoes metathetical reactions in benzene with a variety of nitrosyl halide complexes. Thus treatment of CpCr(NO) ₂X (X = NO₃, NO₂, I, n¹-C₅H₅, or BF₄), CpMn(CO) (NO)I, CpCo(NO)I, and [CpMo(NO) I₂] ₂ with I in 1:1 stoichiometries affords the respective dimeric compounds [CpCr (NO) ₂]₂, [CpMn (CO) (NO) ] ₂, [CpCo(NO)] ₂ and [CpMo (NO) I] ₂ . These latter conversions probably proceed via thermally unstable hydrido complexes. The chromium dimer also results from the reaction [CpCr(NO)₂ (CO)]PF₆ with the aluminum reagent and reacts further with I to produce in low yields a mixture of Cp₂Cr₂ (NO) (NH₂), Cp₂Cr₂ (NO) ₂ (NH₂)₂, and Cp₂Cr₂ (NO) ₂~ (NH₂)(OH). In a similar manner, Fe(NO) ₃Cl is converted by I to Fe₂ (NO) ₄ (NH₂)₂. Reduction of [CpCr(NO) ₂]₂ with BH₃ and with LiEt₃BH produces the same three bimetallic products as when I serves as the reducing agent, and in comparably low yields. However, with LiEt₃BH as reductant the complexes CpCr(NO) ₂Et and Cp₂Cr₂ (NO) ₃ (EtNBEt₂) are also formed, reflecting unprecedented modes of reactivity of the hydridoborate. An x-ray crystallographic analysis of the new Cp₂Cr₂ (NO) ₃ (EtNBEt₂) complex has been performed. The most chemically interesting feature of the molecular structure is the novel EtNBEt₂ ligand which is coordinated via N in a symmetrical fashion to the two Cr atoms. The coordination environment around N is that of a distorted tetrahedron, but the N-B distance of 1.459(5) & suggests some degree of multiple bonding between these two atoms. Such an inference is consistent with the stability of the complex and its spectroscopic properties. The preparation and characterization of several organometallic hydridonitrosyl complexes, i.e. CpMo(NO)₂H and [Cp₂M₁M₂ (NO) ⁴H] ⁺X⁻ (M₁ = M₂ = Mo, W; M₁ = Mo, M₂ = W: X = BF₄ and/or PF₆) are described. The monometallic hydride is prepared by reduction of CpMo(NO)₂Cl with I, while the homonuclear bimetallic cations are formed upon reaction of CpM(NO)₂H (M = Mo, W) with 0.5 equivalents of a hydride abstraction agent such as Ph₃C⁺X⁻ or C₇H₇BF₄ in CH₂Cl₂. The heteronuclear cation can be prepared by the reaction of CpMo(NO)₂Cl with AgBF₄ to produce CpMo(NO)₂ ⁺BF₄⁻, which may then be reacted with CpW(NO)₂H to yield the cation. Attempts to deprotonate these cations with a variety of bases result in cleavage of the metal-metal bond to yield the hydride and a monometallic cation of the type CpM(NO)₂(L)⁺ (where L is the base used). The failure of the attempted deprotonations led to an examination of the Lewis base properties of CpW(NO)₂H and of the Lewis acid properties of CpW(N0)₂⁺. Specifically, the interaction of CpW(NO)₂H with a variety of soft (i.e. Cr(CO)₅, W(CO)₅, (MeCp)Mn(CO)₂, HgCl₂, and CdCl₂), borderline (i.e. ZnCl₂), and hard (i.e. H+, AlCl₃, and BEt₃) Lewis acids is observed spectroscopically. The observed Lewis base characteristics of CpW(NO) ₂H are discussed in light of these results, and when combined with the Lewis acid properties of CpW(NO)₂+, it is possible to rationalize the failure to prepare the dimers [CpM(NO)₂]₂ (M = Mo, W) via the desired route. / Science, Faculty of / Chemistry, Department of / Graduate

Thesis advisor: Jeffery A. Byers / This dissertation describes the design and logic that went into the development of Suzuki-Miyaura cross-coupling reactions catalyzed by iron-based complexes. Chapter 1 provides an overview into the field of iron cross-coupling and the comparison to state-of-the art nickel-based systems. A combination of methodology development and mechanistic insight will be discussed. Chapter 2 describes the initial discovery and optimization of a Suzuki-Miyaura cross-coupling reaction between alkyl halides and unactivated arylboronic pinacol esters catalyzed by an iron cyanobis(oxazoline) complex. Chapter 3 discusses the extension of the catalytic system developed in Chapter 2 to an enantioselective reaction to afford chiral 1,1-diarylalkanes. The dissertation concludes with Chapter 4 which describes the development of a C³-C³ Suzuki-Miyaura reaction catalyzed by a β-diketiminate iron complex. Ligand design and mechanistic studies are discussed here to provide insight into the mechanistic intricacies of the reaction and its effect on future reaction development. / Thesis (PhD) — Boston College, 2021. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

The synthesis and characterization of the first series of tetra-NHC-Ag(I)-X cubane clusters are reported. The clusters were characterized with 1H and 13C NMR spectroscopy, ESI-TOF MS, and single crystal X-ray diffraction. Crossover experimental data were consistent with intramolecular exchange, which can be visualized by a molecular rotating type mechanism. Additionally, -NHC Zr(IV) pincer type complexes were synthesized and characterized with 1H and 13C NMR spectroscopy, CHN combustion analysis, and X-ray crystallography. A large rate effect was observed based on the halogen and metal center for the hydroamination/cyclization of unactivated aminoalkenes. Zirconium based pincers provided faster reaction rates than their hafnium counterparts (Zr>Hf). Precatalysts with iodide ligands provided faster reaction rates than their bromide and chloride counterparts (I>Br>Cl). The mechanism of hydroamination for Zr(IV) -NHC complexes was also investigated for bis(iodide) and bis(amido) ligand classes. A full kinetic analysis of substrate and precatalyst have been identified along with the formation of small amounts of an oxidized product. The proposed mechanism contains an imido-type intermediate whose formation depends greatly on which set of ligand class is used.

No description available.

by Man-Hang Chan. / Thesis submitted in 1997. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references. / Abstract also in Chinese. / Contents --- p.i / Acknowledgements --- p.iii / Abstract --- p.iv / 摘要 --- p.v / Abbreviations --- p.vi / Chapter CHAPTER I --- INTRODUCTION / Chapter I.1 --- "Organometallic chemistry of group 11 elements (Cu, Ag, Au)" --- p.1 / Chapter I.1.1 --- Organocopper(I) compounds --- p.3 / Chapter I.1.2 --- Organosilver(I) compounds --- p.5 / Chapter I.1.3 --- Organogold(I) compounds --- p.7 / Chapter I.2 --- Dimethylpyrazine as a ligand precursor --- p.9 / Chapter I.3 --- Objective of this work --- p.11 / Chapter I.4 --- References --- p.13 / Chapter CHAPTER II --- METALLATION OF DIMETHYLPYRAZINE / Chapter II. 1 --- Introduction --- p.17 / Chapter II. 1.1 --- N-functionalized alkyl ligands --- p.17 / Chapter II. 1.2 --- Synthetic methods --- p.18 / Chapter II. 1.3 --- Synthesis of alkyl ligands with N-functionality --- p.20 / Chapter II.2 --- Results and discussion --- p.22 / Chapter II.2.1 --- "Metallation of 2,3-dimethylpyrazine" --- p.22 / Chapter II.2.2 --- "Metallation of 2,5-dimethylpyrazine" --- p.26 / Chapter II. 2.3 --- "Metallation of 2,6-dimethylpyrazine" --- p.29 / Chapter II.2.4 --- Characterization of compounds --- p.34 / Chapter II. 3 --- Experimental --- p.51 / Chapter II. 4 --- References --- p.57 / Chapter CHAPTER III --- SYNTHESIS AND STRUCTURE OF COPPER(I)AND SILVER(I) COMPOUNDS / Chapter III.l --- Introduction --- p.59 / Chapter III.1.1 --- Synthesis of Group 11 metal alkyl complexes --- p.59 / Chapter III.1.2 --- Structures of Group 11 metal alkyl complexes --- p.61 / Chapter III.2 --- Results and Discussions --- p.63 / Chapter III.2.1.1 --- Synthesis of [Cu{CH(ButMe2Si)C5H4N-2}]4 --- p.63 / Chapter III.2.1.2 --- Reaction of [PictLi] with AgBF4 and AI --- p.64 / Chapter III.2.1.3 --- Characterization of compounds --- p.65 / Chapter III.2.1.4 --- Molecular structure of[Cu{CH(ButMe2Si)C5H4N-2}]4 --- p.67 / Chapter III.2.2 --- Synthesis of [Cu{C(Ph)(SiMe3)C5H4N -2}]2 --- p.73 / Chapter III.2.3.1 --- Reaction of CuI with [DZ´حLi2] and [DZLi2] --- p.73 / Chapter III.2.3.2 --- Reaction of CuI with [DZ'Li] --- p.75 / Chapter III.2.4 --- Characterization of compounds --- p.75 / Chapter III.2.5 --- Attempted reaction of [Q'Li(TMEDA)] with CuCI and CuCl2 --- p.77 / Chapter III. 3 --- Experimental --- p.78 / Chapter III. 4 --- References --- p.87 / Appendix --- p.89