<p> Metal containing complexes have been used to catalyze various organic transformations for the past few decades. The success of several mononuclear catalysts led to transition metal catalysts used in pharmaceuticals, environmental, and industrial processes. While mononuclear complexes have been used extensively, bimetallic systems have received far less attention. Bimetallic or polynuclear sites are commonly found in metalloenzymes that perform elegant transformation in biological systems, underlying their significance. Inorganic chemists take inspiration from nature and design model bimetallic complexes to further study this cooperativity effect. A bimetallic platform offers many structural and functional differences such as the identity of the metal atoms and the bonding interactions between metals, which have been reflected in their unique catalytic ability and reactivity. </p><p> This dissertation encompasses work related to the computational study of metal-metal interactions of bimetallic systems, the ¹H NMR study of stereochemical and conformational changes in solution of <i> N,N'</i>-diarylformamidines, the synthesis of dizinc formamidinate complexes, and the synthesis and catalytic ability of dicopper formamidinate complexes. </p><p> In the first part, DFT calculations are used to study factors that influence metal-metal bond lengths in various complexes. Several experimentally obtained X-ray crystal structures were used as the basis for the study. Differences in metal-metal separations were investigated through various functionals, indicating the importance of charge, orbital interactions, and formal bond order. BH&amp;HLYP SDD/aug-CC-PVDZ geometry optimizations of octahalodimetalate anions Tc₂X₈^n- (X = Cl, Br; n=2, 3), Re₂X₈^2- (X = Cl, Br), and Mo₂Cl₈^4- reproduced M-M bond distance trends observed experimentally. The study demonstrated that the increase in &sigma; and &pi; bond strength resulted in the shortening in Tc-Tc bond distance from Tc₂X₈^2- to Tc₂X₈^3-, which was further supported by the short Mo-Mo bond in the Mo₂Cl₈^4- ion. This study was expanded further through the inclusion of [M₂Cl₄(PMe₃)₄]ⁿ⁺ (M = Tc, Re, n = 0-2) and [Mo₂E₄]^n- (E = HPO₄ or SO₄, n = 2-4), allowing a systematic study on the role of charge on the metal atoms. PBEO SDD/aug-CC-PVDZ calculations revealed that both formal bond order and formal charge on the metal atoms dictate the trends in M-M bond strength. </p><p> The second half of this dissertation focuses on the synthesis and characterization of bimetallic Zn- and Cu-formamidinate complexes. The stereochemical exchange of substituted <i>N,N'</i>-diarylformamidines were studied through ¹H NMR in various solvents. Alkyl substituents placed on the ortho positions were found to shift the isomeric equilibrium in solution through destabilization of the hydrogen-bond dimer evident in X-ray crystal structures. The Z-isomer of substituted <i>N,N'</i>-diarylformamidines is observed in CDCl₃, C₆D₆, and DMSO-d₆ when the ligands feature significant steric hinderance. Similar ortho substituted <i> N,N'</i>-diarylformamidines were also used to enforce steric interactions to limit the nuclearity of Zn-formamidinate complexes. Various dizinc formamidinate complexes were synthesized through direct and transmetalation routes. NMR and mass spectrometry were used alongside X-ray crystal structures to fully characterize the dizinc complexes. Dicopper formamidinates formed through a transmetallation route were synthesized and feature distinct short Cu^&hellip;Cu separations thought to be brought about by metalophillic interactions. Preliminary results suggest catalytic ability of dicopper formamidinates in cyclopropanation and aziridination of styrene with various diazo compounds. The catalytic activity suggests the formation of dicopper carbene and nitrene intermediates, of which only few published experimentally observed examples exist in the literature.</p><p>

The theoretical and practical aspects of the sensitivity that can be achieved in a flow injection manifold with on-line chemical reactions are investigated with a view to decreasing the detection limits. Optimization of the common manifold configurations, normal single line, double line and reverse single line, was carried out by varying the parameters of flow rate(s), injected volume, reagent concentration and manifold length. The reaction of iron(II) with 1,10-phenanthroline was used for the comparison. Ascorbic acid was added to both sample and reagent to avoid side reactions of 1,10-phenanthroline and iron(III). Results showed that manifold and confluence point geometry affected peak height. A sensitivity comparison, using a 21 point calibration, showed that the manifold sensitivity is similar but that the reverse single line $>$ double line $>$ normal single line. The double line manifold has the best detection limit (10 ng mL$\sp{-1})$ due to the absence of a refractive index effect. Experiments were performed to look at the use of solid molybdate reagent columns for the determination of phosphate. Solid columns without any support were found to be very unstable. Stability was improved by the addition of 5 $\mu$m silica but it was still not reproducible enough. Precipitation of barium molybdate within a cation exchange resin did produce better reproducibility but the complexity added made it impractical. Membrane reagent introduction for the determination of phosphate and chloride was investigated. Nafion cation exchange tubing was used for the introduction of acid and hydrazinium ion for phosphate, and acid, iron(III) and thiocyanate and mercury(II) for chloride. Molybdate was introduced for phosphate determination using a supported liquid membrane of tri-butyl phosphate in n-heptane. Sensitivity was improved for the phosphate determination but not for the chloride determination. The use of an ammonia permeation tube was studied for calibration in flow injection. Nessler's reagent was used for the determination. Release rate temperature variation and day to day reproducibility were investigated. Analysis of a sample of pond water was achieved using the permeation tube for on-line, zero dilution, standard additions calibration.

Thesis (Ph.D.)--Lehigh University, 2009. / Adviser: Tianbo Liu.

Thesis (Ph.D.)--Brown University, 2008. / Source: Dissertation Abstracts International, Volume: 69-06, Section: B, page: 3583. Adviser: William Trenkle. Includes bibliographical references.

Thesis--Ph. D., University of Hong Kong. / Mimeographed.

<p> Transition-metal catalysis has enabled the development of an unprecedented number of mild and selective C-C bond-forming reactions. We sought to access the reactivity of palladium and nickel catalysts for two types of transformations: conjugate allylations and sp³-sp³ cross-coupling reactions. </p><p> Conjugate allylation of malononitriles was evaluated with N-heterocyclic carbene-ligated palladium complexes. The allylation was found to yield a variety of mono-allylated products. These results are in contrast to the bis-allylation of malononitriles using other palladium-based catalysts. Additionally, conjugate addition of &alpha;,&beta;-unsaturated <i>N</i>-acylpyrroles was found to be accelerated in the presence of sulfoxide substitution on the pyrrole ring. These substrates are lead compounds for the development of an enantioselective allylation reaction. </p><p> Transition metal-catalyzed cross-coupling reactions have become standard practice in organic synthesis. Recent advances in alkyl-alkyl couplings have been transformative in the way organic chemists approach the construction of target molecules. This dissertation focuses on the development of stereospecific sp³-sp³ cross-coupling reactions. We discovered that in the presence of nickel catalysts, secondary benzylic ethers were found to undergo stereospecific substitution reactions with Grignard reagents. Reactions proceeded with inversion of configuration and high stereochemical fidelity. This reaction allows for facile enantioselective synthesis of biologically active diarylethanes from readily available optically enriched carbinols. </p><p> Subsequently, this reaction was expanded to dialkylzinc reagents and the first stereospecific Negishi cross-coupling reaction of secondary benzylic esters was developed. A series of traceless directing groups were evaluated for their ability to promote cross-coupling with dimethylzinc. Esters with a chelating thioether derived from commercially-available 2-(methylthio)acetic acid were found to be the most effective. The products were formed in high yield and with excellent stereospecificity. A variety of functional groups were tolerated in the reaction including alkenes, alkynes, esters, amines, imides, and <i>O</i>-, <i>S</i>-, and <i>N</i>-heterocycles. The utility of this transformation was highlighted in the enantioselective synthesis of a retinoic acid receptor (RAR) agonist.</p>

<p> Several metal-tetracyanoethylene (TCNE) compounds, including the [bis(pentamethylcyclopentadienyl)iron(III)][tetracyanoethylene], [FeCp*²][TCNE], family of molecule-based magnets and two cyanide based MBMs were investigated by pressure dependent DC magnetic measurements. The 0-D electron transfer salts: [FeCp*²][TCNE], ferromagnetic [FeCp*²][TCNQ] (TCNQ = 7,7,8,8-tetracyanoquinodimethane), metamagnetic [FeCp*²][TCNQ], [FeCp*²][HCBD] (HCBD = hexacyanobutadiene), and [FeCp*²][DDQ] (DDQ = 2,3-dichloro-5,6-dicyano-p-benzoquinone) exhibited an array of magnetic behavior both at ambient and applied pressure. [FeCp*²][TCNE] and [FeCp*²][HCBD] exhibited weak ferromagnetism above 4.2 and 3.1 kbar, respectively. The ferromagnetic polymorph of [FeCp*²][TCNQ] displayed linear increase to the critical temperature, <i>T</i>_c, and the bifurcation temperature, <i>T</i>_b, reaching 5.01 and 5.46 K, respectively at 10.3 kbar. The coercive field, <i>H</i>_cr, displayed exponential-like increase, reaching 550 Oe at 10.3 kbar. The metamagnetic polymorph of [FeCp*²][TCNQ] displayed linear increase of the Tc at low applied pressure, reaching 2.90 at 2.9 kbar, then transitioned to a paramagnetic state at further applied pressure. [FeCp*²][HCBD] transitioned from a paramagnetic state at ambient pressure to a weak ferromagnetic state at 3.1 kbar with a <i>T</i>_c, <i>H</i>_cr, and <i>H</i>_c of 2.46 K, 25 Oe, and 2,200 Oe, respectively. The <i>T</i>_c and <i>H</i>_c then increased linearly with further applied pressure to 4.80 K and 10,000 Oe, while the <i>H</i>_cr increased exponentially to 795 Oe, at 11.4 kbar. [FeCp*²][DDQ] exhibited paramagnetic behavior at ambient and applied pressures up to 9.2 kbar. The structurally related 2-D Mn^II(TCNE)I(H₂O) and 3-D MnII(TCNE)_3/2(I₃)_1/2, showed significant increases to the <i> T</i>_c, T_b, and <i>H</i>_cr with applied pressure. A high- and low-pressure regions were observed for Mn^II(TCNE)I(H₂O). 2-D [Ru₂(O₂CBu^t)₄][M(CN)₆] &middot; H2O (M = Fe, Cr) displayed suppression of hysteretic properties at high applied pressure and irreversibility of the suppression. A Mean Field (MF) analysis of three structurally related non-cubic Prussian blue analogues (PBA) was performed to assess the intensity of their coupling modes. These values were framed by the reinvestigation of several known cubic PBAs and comparing the coupling intensities, as well as evaluating the MF theory in the context of these structures as several had been evaluated by other means.</p>

<p> Vanadium oxide-fluorides can exhibit properties of piezoelectricity, second harmonic generation (SHG) activity, electrochemical activity, and other phenomena. The first two properties derive from the second-order and Jahn-Teller distortions, respectively, of d⁰ and d¹ vanadium; the electrochemistry derives from the reduction of V^V to V^IV,III,II. </p><p> An examination of the immediate environment of a vanadium cation facilitates an understanding of how a cation influences the structure of a compound and its resulting properties. In the inorganic hydrate CuVOF₄(H₂O)₇, the CuVOF₄(H₂O)₆ basic-building unit (BBU) has a &Lambda;-shape that compels polar packing in a structure that has SHG properties. The compound is a very rare example of a carbonless, SHG-active molecular crystal. Influences for its packing are reasoned with principles previously used within organic molecular crystallography. </p><p> The early transition metals (ETMs) of vanadium, niobium, and molybdenum within compounds of formulae K₁₀(M₂O_nF_11-n)X (M = V^V, Nb^V, n = 2, M = Mo^VI, n = 4; X = halide) show a related packing motif of &Lambda;-shaped BBUs in different structures. Owing to the absence or presence of &Lambda;-shaped BBUs, these heterotypical structures crystallize decidedly into SHG-inactive or SHG-active forms when M = V^V or M = Nb^V, Mo^VI, respectively. The future use and development of &Lambda;-shaped BBUs within solid-state systems can result in SHG-active materials. </p><p> The material CuVOF₄(H₂O)₇ presents an interesting coordination: the late transition metal (LTM, Cu^II) coordinates solely to the oxide anion of the vanadyl cation owing to hard-soft acid-base (HSAB) properties. The materials Na₂[M(H₂O)₂][V₂O₄F₆] (M^II = Co, Ni, Cu) show the LTM coordinates solely to the oxide anions of the V^V cation while the alkali cation (Na^I) coordinates solely to the fluoride anions. These HSAB properties were used to generate layers of hard or soft cation/anion rich regions in the electrochemically-active double wolframite AgNa(VO₂F₂)₂. </p><p> These structure-property examinations of solid state vanadium oxide-fluorides are presented as principles for (i) fundamental understanding of ETM and BBU crystallographic environments, (ii) materials discovery for fundamental investigations, (iii) materials design, and (iv) materials for use in SHG, piezoelectric, and electrochemical processes.</p>

<p> Radical chemistry has attracted a large amount of research interest over the last few decades and radical reactions have recently been recognized as powerful tools for organic synthesis. The synthetic applications of radicals have been demonstrated in many fields, including in the synthesis of complex natural products. Radical reactions have a number of inherent synthetic advantages over their ionic counterparts. For example, they typically proceed at fast reaction rates under mild and neutral conditions in a broad spectrum of solvents and show significantly greater functional group tolerance. Furthermore, radical processes have the capability of performing in a cascade fashion, allowing for the rapid construction of complex molecular structures with multiple stereogenic centers. To further enhance the synthetic applications of radical reactions, current efforts are devoted toward the development of effective approaches for the regioselective control of their reactivity as well as stereoselectivity, especially enantioselectivity, a challenging issue that is intrinsically challenged by the "free" nature of radical chemistry. </p><p> This research has identified a fundamentally new approach to radical reactions based on the concept of metalloradical catalysis (MRC) for controlling the stereoselectivity of both C- and N-centered radical reactions. Cobalt(II) porphyrins [Co(Por)], are stable metalloradicals, and have been shown to enable the activation of diazo reagents and azides to cleanly generate C- and N-centered radicals, respectively, with N₂ as the only byproduct in a controlled and catalytic manner. In addition to the radical nature of [Co(Por)], the low bond dissociation energy of Co-C/Co-N bonds plays a key role in the successful turnover of the Co(II)-based catalytic carbene and nitrene transfers. Through the support of porphyrin ligands with tunable electronic, steric, and chiral environments, this general concept of Co(II)-based metalloradical catalysis (Co-MRC) has been successfully applied to the development of various radical processes that enable stereoselective carbene and nitrene transfers. </p>

Thesis (Ph. D.)--Indiana University, Dept. of Chemistry, 2008. / Title from home page (viewed Oct 7, 2009). Source: Dissertation Abstracts International, Volume: 70-02, Section: B, page: 1017. Adviser: Dongwhan Lee. Includes supplementary digital materials.