The Synthesis and Reactivity of New Pnictogen(III) Cations

Chelating nitrogen based ligands are well known for their use with transition metals while their chemistry with p-block elements has been relatively underdeveloped. This thesis examines the structure, bonding and reactivity of group 15 elements supported by a pyridyl tethered 1,2-bis(imino)acenaphthene (“clamshell”) and various homo- and heteroleptic guanidinate frameworks. The unique “clamshell” ligand contains a pendant Lewis base and has been used to support N-heterocyclic phosphenium and arsenium cations. Reactivity studies with the phosphorus analogue demonstrate the ability of the ligand to act as a Lewis base, while the phosphorus centre provides a Lewis acidic site, showing the amphoteric nature of such a molecule. Cobaltocene has been used as a new one-electron reductant in the facile, high yielding synthesis of a diaminochloroarsine supported by the “clamshell” ligand. Unfortunately this method was not suitable for all Group 15 elements and resulted in low yields for phosphorus and insoluble black material for antimony and bismuth. In the absence of a reductant the “clamshell” ligand can be used to form hypervalent donor-acceptor complexes with heavy main group elements (Sn, Sb and Bi). The addition of a salt metathesis reagent to the hypervalent Sb and Bi complexes results in base-stabilized SbCl2+ and BiCl2+ cations. A series of diaminochlorophosphines has been synthesized with various dianionic guanidinate ligands, and their reluctancy to release a chloride ion using halide abstracting reagents has been noted. A comprehensive study of their reactivity has been completed and the following were observed: (i) that the chloride ion could be removed with the addition of a chelating base; (ii) that carbodiimide can be eliminated chemically and thermally from the four-membered ring; and, (iii) that a rare ring expansion by the insertion of a chloro(imino)phosphine into a P–N bond of the P–N–C–N framework takes place. The analogous chemistry with heavier pnictogens to form diaminochloropnictines does not occur; rather the products are diaminodichloropnictines where the guanidinate ligand is monoanionic. Halide abstraction from these molecules is facile for As and Sb and the addition of a chelating base allows for the removal of the second chloride ion to give base-stabilized dicationic species

Implication for Functions of the Ectopic Adipocyte Copper Amine Oxidase (AOC3) from Purified Enzyme and Cell-Based Kinetic Studies

AOC3 is highly expressed in adipocytes and smooth muscle cells, but its function in these cells is currently unknown. The in vivo substrate(s) of AOC3 is/are also unknown, but could provide an invaluable clue to the enzyme's function. Expression of untagged, soluble human AOC3 in insect cells provides a relatively simple means of obtaining pure enzyme. Characterization of enzyme indicates a 6% titer for the active site 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor and corrected kcat values as high as 7 s−1. Substrate kinetic profiling shows that the enzyme accepts a variety of primary amines with different chemical features, including nonphysiological branched-chain and aliphatic amines, with measured kcat/Km values between 102 and 104 M−1 s−1. Km(O2) approximates the partial pressure of oxygen found in the interstitial space. Comparison of the properties of purified murine to human enzyme indicates kcat/Km values that are within 3 to 4-fold, with the exception of methylamine and aminoacetone that are ca. 10-fold more active with human AOC3. With drug development efforts investigating AOC3 as an anti-inflammatory target, these studies suggest that caution is called for when screening the efficacy of inhibitors designed against human enzymes in non-transgenic mouse models. Differentiated murine 3T3-L1 adipocytes show a uniform distribution of AOC3 on the cell surface and whole cell Km values that are reasonably close to values measured using purified enzymes. The latter studies support a relevance of the kinetic parameters measured with isolated AOC3 variants to adipocyte function. From our studies, a number of possible substrates with relatively high kcat/Km have been discovered, including dopamine and cysteamine, which may implicate a role for adipocyte AOC3 in insulin-signaling and fatty acid metabolism, respectively. Finally, the demonstrated AOC3 turnover of primary amines that are non-native to human tissue suggests possible roles for the adipocyte enzyme in subcutaneous bacterial infiltration and obesity

Anion Sensing with a Blue Fluorescent Triarylboron-Functionalized Bisbenzimidazole and Its Bisbenzimidazolium Salt

A blue fluorescent <i>p</i>-dimesitylboryl-phenyl-functionalized 1,3-bisbenzimidazolyl benzene molecule (<b>1</b>) has been synthesized in high yield by Stille coupling of bisbenzimidazolyl bromobenzene with <i>p</i>-BMes₂-SnBu₃-benzene. Methylation of <b>1</b> led to the formation of the bisbenzimidazolium salt (<b>2</b>). The utility of both <b>1</b> and <b>2</b> in sensing CN^– and halide (F^–, Cl^–, Br^–, and I^–) was examined, and it was found that only the small fluoride and cyanide anions were able to bind to the boron atom with binding constants in the range of 2.9 × 10⁴ to 5 × 10⁵ M^–1. Computational studies provided insight into the photophysical properties of the molecules and verified that a charge-transfer process is quenched in these “turn-off” molecular sensors

Blue Fluorescent Deoxycytidine Analogues: Convergent Synthesis, Solid-state and Electronic Structure, and Solvatochromism

We report the synthesis and photospectroscopic characterisation of intrinsically fluorescent triazole-appended cytidines. Fluorescence was found to be highly dependent on solvent conditions. X-Ray crystallographic data show the proton of the exocyclic amine of the nucleobase and the triazole N(3) engaged in a H-bond

Synthesis, Reactivity, and Computational Analysis of Halophosphines Supported by Dianionic Guanidinate Ligands

The reported chemistry and reactivity of guanidinate supported group 15 elements in the +3 oxidation state, particularly phosphorus, is limited when compared to their ubiquity in supporting metallic elements across the periodic table. We have synthesized a series of chlorophosphines utilizing homo- and heteroleptic (dianionic)­guanidinates and have completed a comprehensive study of their reactivity. Most notable is the reluctancy of these four-membered rings to form the corresponding <i>N</i>-heterocyclic phosphenium cations, the tendency to chemically and thermally eliminate carbodiimide, and the scarcely observed ring expansion by insertion of a chloro­(imino)­phosphine into a P–N bond of the P–N–C–N framework. Computational analysis has provided corroborating evidence for the unwillingness of the halide abstraction reaction by demonstrating the exceptional electron acceptor properties of the target phosphenium cations and the underscoring strength of the P–X bond

Synthesis, Reactivity, and Computational Analysis of Halophosphines Supported by Dianionic Guanidinate Ligands

The reported chemistry and reactivity of guanidinate supported group 15 elements in the +3 oxidation state, particularly phosphorus, is limited when compared to their ubiquity in supporting metallic elements across the periodic table. We have synthesized a series of chlorophosphines utilizing homo- and heteroleptic (dianionic)­guanidinates and have completed a comprehensive study of their reactivity. Most notable is the reluctancy of these four-membered rings to form the corresponding <i>N</i>-heterocyclic phosphenium cations, the tendency to chemically and thermally eliminate carbodiimide, and the scarcely observed ring expansion by insertion of a chloro­(imino)­phosphine into a P–N bond of the P–N–C–N framework. Computational analysis has provided corroborating evidence for the unwillingness of the halide abstraction reaction by demonstrating the exceptional electron acceptor properties of the target phosphenium cations and the underscoring strength of the P–X bond

Theoretical and experimental investigations of ligand exchange in guanidinate ligand systems for group 13 metals

The ligand exchange of guanidinate ligands between metal centres can play an important role in guanidinate chemistry, and ligand exchange between aluminium centres will form a dimeric intermediate. The synthesis and characterization of the dimer [Me2NC(NiPr)2]2Al2Cl4 (1) is reported here: compound 1 crystallizes with a twisted boat conformation of its dimer ring. This compound decomposes to monomers at room temperature over four days, or within 18 hours at 90 °C. We undertook a detailed computational characterization of the reaction pathway, which supported the dimer structure and subsequent monomer formation. The ligand exchange route was also exploited for the synthesis of [MeC(NiPr)2]2AlCl (2), [EtC(NiPr)2]2AlCl (3), [MeC(NiPr)2]2GaCl (5), and [Me2NC(NiPr)2]2GaCl (6)

Dechlorinated Analogues of Dechlorane Plus

Degradation products of the chlorinated additive flame retardant Dechlorane Plus (DP) have been discovered globally. However, the identity of many of these species remains unknown due to a lack of available analytical standards, hindering the ability to quantitatively measure the amounts of these compounds in the environment. In the present study, synthetic routes to possible dechlorinated DP derivatives were investigated in an effort to identify the environmentally significant degradation products. The methano-bridge chlorines of <i>anti</i>- and <i>syn</i>-DP were selectively replaced by hydrogen atoms to give six new hydrodechlorinated DP analogues. The identity and absolute configuration of all of these compounds were confirmed by GC-MS, NMR spectroscopy, and X-ray diffraction studies. These compounds were observed in sediment samples from streams and rivers in relatively rural areas of Ontario and are thus environmentally relevant