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<p> A new rigid, dianionic ligand, 4,5-bis(2,6-diisopropylanilido)-2,7-di-tert-butyl-9,9-dimethylxanthene {[XA₂]}, has been designed for use in the chemistry of the actinides. Pro-ligand H2[XA₂] (1) was synthesized by the Hartwig-Buchwald coupling of 4,5-dibromo-2,7-di-tert-butyl-9,9-dimethylxanthene with 2,6-diisopropylaniline. </p> <p> Stable alkali metal salts of the [XA₂] ligand, K₂(dme)₂[XA₂] (2) and Na₂[XA₂] (3), were accessible by deprotonation of H₂[XA₂] with KH or NaH in dme or toluene, respectively. The thermally unstable lithium salt of McConville's 2,6-bis(2,6diisopropylanilidomethyl)pyridine {Li₂[BDPP], 4} was isolated by deprotonation of pro-ligand H₂[BDPP] with nBuLi or LiCH₂SiMe₃ in hexanes at low temperature. Reaction of [ThCl₄(dme)₂] with Li₂[BDPP] or M₂(dme)_n[XA₂] (M = K, n = 2; M = Na, n = 0) resulted in the formation of pentagonal bipyramidal [LThCl₂(dme)] complexes {L = [BDPP], 5; [XA₂], 6}. Subsequent reaction of the dichloride complexes with LiCH₂SiMe₃ gave base-and salt-free dialkyl complexes [LTh(CH₂SiMe₃)₂] {L = [BDPP], 9; [XA₂], 10}, which are stable for days in solution at 90 and 70 °C, respectively. Reaction of 5 with LiNEt₂ or 10 with H₂NPh provided [(BDPP)Th(NEt₂)₂] (11) and [(XA₂)Th(NHPh)₂] (28), respectively. </p> <p> An alternative route to [(BDPP)ThCl₂(dme)] (5) and [LTh(CH₂SiMe₃)₂] (9 and 10) involved combination of two or four equivalents of LiCH₂SiMe₃ with [ThCl₄(dme)₂], followed by addition of H₂L. These reactions likely proceed by alkane elimination from dialkyl or tetraalkyl thorium intermediates. The solid-state structure of [(BDPP)Th(CH₂SiMe₃)₂] (9) suggests the presence of α-agostic C-H-Th interactions for both alkyl groups. In solution, 9 and 10 exhibit temperature-dependent ¹J_C-H coupling constants for ThCH₂, consistent with an equilibrium between products participating in aagostic C-H-Th bonding to a greater or lesser extent, with more agostic products favored at lower temperatures. Reaction of Li₂[BDPP] (4) with [(BDPP)ThCl₂(dme)] (5) at 0 °C, or the reaction of [(BDPP)Th(CH₂SiMe₃)₂] (9) with H₂[BDPP] at 100 °C resulted in the formation of extremely sterically encumbered [Th(BDPP)₂] (8), which adopts a highly distorted six-coordinate geometry with the four anilido groups arranged in an approximate tetrahedron around thorium. A his-ligand complex was not accessible with the [XA₂] ancillary ligand, presumably due to increased ligand rigidity. </p> <p> Addition of two equivalents of PhCH₂MgCl to [LThCl₂(dme)] yielded solvent-free [LTh(CH₂Ph)₂] {L = [XA₂] (12) and [BDPP] (13)]. The ¹J_C-H coupling constants in both complexes {120 and 139 Hz for 12; 127 and 138 Hz for 13} are indicative of η¹- and η²- or η³-coordinated benzyl ligands in solution; polyhapto benzyl coordination was also observed in the solid state. </p> <p> Reaction of [LThCl₂(dme)] with two equivalents of nBuLi provided highly soluble [LTh(nBu)₂] {L = [BDPP] (14), [XA₂] (15)]. These β-hydrogen-containing compounds are remarkably thermally stable, showing no sign of decomposition after days at 60 and 80 °C, respectively. Combination of [(BDPP)ThCl₂(dme)] (5) with three equivalents of MeLi yielded the thorium trimethyl 'ate' complex [(BDPP)ThMe₃{Li(dme)}] (16), which underwent thermal decomposition over 3 days at room temperature to produce the metalated complex [(BDPP*)Th(µ-Me)₂Li(dme)] (17) {BDPP* = 2,6-{NC₅H₃(CH₃NAr)(CH₂N {C₆H₃iPr(CMe₂)-2,6})}; Ar = 2,6-diisopropylphenyl; donor atoms in BDPP* are underlined}. Reaction of two equivalents of complex 16 with one equivalent of [(BDPP)ThCl₂(dme)] (5) yielded the dimethyl complex [(BDPP)ThMe₂] (18) which decomposes rapidly at room temperature to form a mixture of unidentified products. Labeling studies using ¹³CD₃ groups revealed that thermal decomposition of 16 and 18 occurs via a straightforward a-bond metathesis pathway. </p> <p> Reaction of [LThCl₂(dme)] with Grignard reagents {MeMgBr, L = [BDPP]; PhCH₂MgCl, L = [XA₂]} resulted, under certain conditions, in halide exhange and adduct formation as evidenced by the solid state structure of [{Th(BDPP)Br(µ-Br)₂Mg(µ-Me)(OEt₂)}₂] (19), or ancillary ligand transfer to magnesium to produce [(XA₂)Mg(dme)] (20). Complex 19 provides insight into the type of intermediates likely involved in undesired halide exchange reactions between d-or f-element halide complexes and Grignard reagents. </p> <p> Reaction of [(XA₂)Th(CH₂Ph)₂] (12) with either one or two equivalents of B(C₆F₅)₃ afforded the first non-carbocyclic actinide alkyl cation, [(XA₂)Th(CH₂Ph)][PhCH₂B(C₆F₅)₃] (21), and a rare example of an actinide dication, [(XA₂)Th][PhCH₂B(C₆F₅)₃]₂ (27). In both 21 and 27 the PhCH₂B(C₆F₅)₃⁻ anion is η⁶-coordinated to thorium. Reaction of neutral dialkyl complex [(XA₂)Th(CH₂SiMe₃)₂] (9) with [Ph₃C][B(C₆F₅)₄] in benzene or toluene at room temperature resulted in the formation of [(XA₂)Th(CH₂SiMe₃)(η⁶-arene)][B(C₆F₅)₄] (arene = C₆H₆, 22; arene = C₇H₈, 23). These complexes were characterized in solution by NMR spectroscopy (21, 22 and 23) and/or in the solid state by X-ray crystallography (22 and 27). In close analogy, [(XA₂)Th(CH₂Ph)₂] (12) reacted with [Ph₃C][B(C₆F₅)₄] in toluene at room temperature to form [(XA₂)Th(η²-CH₂Ph)(η⁶-C₇H₈)][B(C₆F₅)₄] (24). In contrast, related [(BDPP)Th(CH₂Ph)₂] (13) reacted with [Ph₃C][B(C₆F₅)₄] to precipitate a mixture of mononuclear and a dinuclear cations; the dinuclear cation was identified as [(BDPP)Th(η²-CH₂Ph)(µ-η¹:η⁶-CH₂Ph)Th(η¹-CH₂Ph)(BDPP)][B(C₆F₅)₄] (25) by X-ray crystallography. Complexes 22, 23, and 24 are rare examples of arene solvent-separated ion pairs, while complex 21 exists as a tight contact ion pair, and dinuclear 25 exhibits a unique benzyl ligand bridging mode. Cations 21-25 and 27 highlight a pronounced tendency for these systems to engage in arene π-coordination. </p> <p> Preliminary reaction studies with both neutral and cationic thorium complexes supported by the [BDPP] and [XA₂] ancillary ligands demonstrated significant activity for olefin polymerization and hydroamination catalysis. Reactions of 9 and 10 with 4 atm. of hydrogen also suggest that the [BDPP] and [XA₂] ligand frameworks may be suitable for the stabilization of thorium hydride complexes. </p> / Thesis / Doctor of Philosophy (PhD)

Thesis (Ph. D.)--Auburn University. / Abstract. Vita. Includes bibliographical references (p. 110-125).

<p> Carbocyclic and heterocyclic compounds are ubiquitous in nature. Therefore, the discovery and development of new ring forming reactions are of paramount interest to synthetic organic chemists. Recently, the intramolecular cyclization of reactive intermediates, such as anions, cations, and radicals have provided a number of new methods by which known and novel ring systems can be constructed. Cyclizations involving tandem, or multiple sequences have gained considerable popularity due to their high overall efficiency and remarkable speed by which these processes can yield complex polycyclic ring systems.</p> <p> Carbenes are another interesting class of reactive intermediates which undergo characteristic reactions. The cyclization reactions of carbenes have not been studied to a significant extent. In particular, the work described in this thesis outlines the only study of the intramolecular cyclization of dioxycarbenes onto a tethered alkyne moiety.</p> <p> The first section of this dissertation details the development of a convenient new class of thermal dioxycarbene precursors, dioxyoxadiazolines I, which display many significant advantages over previously used sources of dioxycarbenes ll. (See Diagram in Thesis)</p> <p> The second section of this dissertation details the use of dioxyoxadiazolines possessing a tethered triple bond for the thermal generation of dioxycarbenes III which are capable of intramolecular cyclization. It was found that the cyclization of a dioxycarbene onto a tethered triple bond results in the regioselective generation, of another reactive intermediate, a 3,3-dioxyvinylcarbene (IV or V, depending on the nature of R'), which can undergo a number of interesting intermolecular reactions. This approach leads to the rapid construction of some interesting and rather complex polycyclic heterocyles which are, in many cases, obtained with high regioselectivity and sometimes even high stereoselectivity. (See Diagram in Thesis)</p> <p> The results described in this thesis mark the discovery and development of a new synthetic methodology which may, by appropriate choice of the starting material, provide a valuable tool for the rapid and selective synthesis of a number of heterocyclic ring systems.</p> / Thesis / Doctor of Philosophy (PhD)

The addition of allyl magnesium and allyl indium reagents to a key TBS protected norbornenyl building block, synthesised in 6-steps from commercially available 1,1-dimethoxy-2,3,4,5-tetrachlorocyclo-pentadiene, has been achieved providing the syn addition products with high diastereoselectivity. The subsequent exposure of the addition products to metathesis conditions, in the presence of ethylene, then provided cis fused [3.0.3]-carbocycles with very high regioselectivity, via a Ring Rearrangement Metathesis (RRM) transformation. The high level of regioselectivity is due to the rearrangement of the metathesis intermediates to give the more thermodynamically stable product This work has been expanded to include [2.2.2]-bicycles, addition of allyl magnesium and indium reagents to a key bicyclo[2.2.2]oct-5-en-2-one has been achieved, giving both diastereoisomers, separable by chromatography. The subsequent exposure of the addition products to optimised metathesis conditions, then provided cis fused [3.3.1] carbocycles with very high regioselectivity, via a RRM transformation. It was found that two possible cyclisation pathways occur under our reaction conditions; pathway (a) will yield a cis-fused [4.0.3]-carbocycle while pathway (b) will deliver the observed [3.3.1]-carbocycle.