The addition of dimethylarsine to hexafluoro-butyne-2 has previously been shown to give the predominantly trans 1:1 adduct, Me₂AsC(CF₃)=C(CF₃)H. In this work, a mechanistic study was made of the addition of dimethylarsine, as well as other Group V hydrides, to hexafluorobutyne-2. This was done to help shed light on the relatively unknown area of noncatalyzed nucleophilic hydride additions to acetylenes. In the course of the mechanistic investigation, the electronic properties of the product adducts became of interest, and consequently ultraviolet and photoelectron spectroscopy were used to study the arsine adducts as well as similiar Group V derivatives. The addition reaction was found to be kinetically controlled by the nucleophilic attack of the arsine molecule on the electron deficient carbon-carbon triple bond. A detailed discussion of the addition stereochemistry is necessary to explain many of the results found in this work, as well as those found by other investigators. Generally the noncatalyzed additions of Group V hydrides to acetylenes are predominantly, though not stereo-specifically, trans additions. Cis kinetic additions are possible under certain circumstances. The ultraviolet absorption found for the 1:1 adducts of Group V hydrides and hexafluorobutyne-2, can be assigned to a n-π* (or n-R) band. An unequivocal choice between the two possibilities cannot be made from the results obtained in this work. These assignments are suggested from experimental data about the upper ground states using photoelectron spectroscopy, the excited state using ultraviolet spectroscopy,and the intensities and solvent effects of the ultraviolet bands. / Science, Faculty of / Chemistry, Department of / Graduate

Current knowledge of mechanistic organometallic chemistry has resulted largely from the study of mononuclear transition metal complexes. The possibility that different primary organometallic processes involving two or more metal centres may exist has been addressed only recendy. Reactivity studies on a simple, well defined binuclear system ought to provide fundamental insights into the nature of such polynuclear primary processes. The binuclear rhodium hydrides {[R₂P(CH₂)nPR₂]Rh(μ-H)}₂ (R = Pri, n = 2-4, 1a-1c; R = OPri, n = 2, 1d) were thus reacted with a variety of organic compounds in an attempt to define primary processes involving two metal centres. The reactions of 1a-c with dihydrogen proceed rapidly to produce fluxional binuclear tetrahydrides whose structure is dependent on the chelate ring size of the diphosphine ligand. The dihydrides also catalyze the hydrogenation of olefins. Two mechanistic pathways for this cycle are proposed to exist as supported by chemical and kinetic evidence. One utilizes binuclear intermediates, the other mononuclear; the latter predominates in the 1b catalyzed system (chelate ring size of six) while the former is favoured in the cycle mediated by la (chelate ring size of five). The reactions of 1a and 1b with 1,3-dienes led to the solid (X-ray diffraction) and solution state characterization of binuclear complexes incorporating bridging dienyl ligands in the previously unobserved μ-ƞ⁴-ϭ and μ-ƞ³-ƞ³ "partial sandwich" bonding modes. A fluxional process interconverting the two bonding modes was observed spectroscopically in the products of the 1a/butadiene reaction and a model accounting for this is proposed. Labelling and alternate synthetic studies, as well as the observation of an intermediate at low temperature, support a mechanism for these reactions which involves the dehydrogenation of the dihydrides followed by further reaction of [(P₂)Rh]₂ with a second equivalent of diene. Bridging amido hydrides of general formula [(P₂)Rh]₂(μ-NR'CH₂R")(μ-H) are produced in the reactions of 1a and 1d with imines (R'N=CHR"). Mechanistic studies reveal that initial ϭ-donation of the imine lone pair; of electrons to one Rh followed by π-coordination of the C=N bond to the other precedes formal insertion of the C=N bond into Rh-H. This proposal is consistent with the results of labelling and kinetic studies, but the crux of its support lies in the spectroscopic observation of two intermediates en route to the product amido hydrides. The specific synthesis of cationic μ-ƞ²-ϭ imine complexes closely related to one of the proposed intermediates in the reaction was carried out to confirm the plausibility of such an intermediate. Reaction of the amido hydrides with dihydrogen was slow in producing free amine and the hydrogen adducts of 1a or 1d, precluding the use of these dihydrides as catalyst precursors in the homogeneous hydrogenation of imines. Reaction of 1a and 1d with nitriles (R"'C=N) produces μ-alkylideneimido hydride complexes of general formula [(P₂)Rh]₂(μ-N=CHR'")(μ-H). One derivative (P₂, R = Pri, n = 2; R"' = CH₃) has been characterized by X-ray crystallography. Further reaction of these complexes with dihydrogen yield the amido hydrides [(P₂)Rh]₂(μ-NHCH₂R"')(μ-H). No intermediates in these reactions were observed, precluding meaningful mechanistic proposals for this stepwise reduction of nitriles as mediated by two metal centres. / Science, Faculty of / Chemistry, Department of / Graduate

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Thesis (Ph. D.)--University of Nevada, Reno, 2008. / "May, 2008." Includes bibliographical references (leaves 110-122). Online version available on the World Wide Web.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 125-130). Also available via the Internet.

Three gas phase alkaline earth molecules were analyzed using dye laser spectroscopy. The A¹Σ⁺ - X¹Σ⁺ transition of gas phase SrS was studied with high resolution techniques. The 0-0, 0-1, 1-1, 2-1, 3-0, 3-2, 4-1, 5-1, and 5-2 bands were rotationally analyzed and spectroscopic constants were determined. The A¹Σ⁺ state was extensively perturbed. Ground state (X¹Σ⁺) constants derived from the analysis of the nine vibrational levels include: ωₑ = 388.2643 cm⁻¹, Bₑ = 0.1208034(33) cm⁻¹, and rₑ = 2.439687(14) Å. Excited state (A¹Σ⁺) constants determined include: Tₑ = 13932.7068(10) cm⁻¹, ωₑ = 339.1454(20) cm⁻¹, Bₑ = 0.1139895(38) cm⁻¹, and rₑ = 2.511601(17) Å. The spectra of calcium and strontium borohydrides were observed using low resolution laser spectroscopy. The spectra were assigned to the òA₁ - Ẋ²A₁ and Ḃ²E - Ẋ²A₁ transitions of CaBH₄ and SrBH₄. The vibrational frequencies of the metal-ligand stretch determined for CaBH₄ were 457 cm⁻¹ (Ẋ²A₁), 473 cm⁻¹ (Ā²A₁), and 465 cm⁻¹ (Ḃ²E). The corresponding SrBH4 frequencies were 399 cm⁻¹, 420 cm⁻¹, and 421 cm⁻¹.

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