No description available.

Tripodal borate ligands, including Tp and Tm, are some of the most widely used in organometallic chemistry and were originally prepared, as anions, from the reaction of the relevant heterocycle with an alkali metal borohydride. However, an alternate route, allowing access to zwitterionic, charge-neutral, scorpionates was recently developed within the Bailey group using tris(dimethylamino)borane as the boron source. This thesis describes the expansion of the borane synthetic route to create new, charge-neutral, zwitterionic, tris(methimazolyl)borate (ZTm) ligands containing B-N, B-O and B-C coordinate bonds. Unusual reactivity with isonitrile donors is also presented which has allowed access to boron substituted anionic Tm ligands from the charge-neutral starting material, (HNMe2)ZTm. Attempts to control the helical chirality of ZTm complexes, by using chiral imidazoline donors on the central boron are also described. The borane synthetic route has allowed access to the novel ligand ZThp, the first example of a tripod based on 2-hydroxypyridine ligand arms. As with Tm, this ligand exhibits helical chirality upon complexation and demonstrates how individual atom hybridisation within the ligand arms affects the helicity and thus the chirality of flexible scorpionate ligands. Coordination studies of both zwitterionic and boron-substituted anionic Tm ligands have shown a tendency for the formation of ‘sandwich’ complexes of the form L2M with some metal precursors, whilst the formation of the corresponding ‘half-sandwich’ complexes of these ligands with ruthenium and rhodium was found to be disfavoured.

Cette thèse porte sur la synthèse et la caractérisation de complexes octaédrique de fer(II) et fer(III) coordinés par un ligand tridente de type scorpionate (symétrie fac) et par trois ligands cyanures. Leur utilisation en tant que metalloligand face à des ions métalliques partiellement bloqués est étudiée. Les ligands cyanures, de par leur caractère ambidente, permettent un accès facile aux espèces hétérobimétalliques. De plus, ces ligands sont connus pour transmettre efficacement l'interaction d'échange magnétique et donc pour favoriser la communication électronique intramoléculaire entre les ions métalliques qu'ils relient. La fonctionalisation des ligands scorpionates permet de contrôler les propriétés électroniques intrinsèques des complexes précurseurs de fer, et donc de moduler les propriétés des espèces polynucléaires obtenues à partir de ces dernières par auto-assemblage. Dans cette thèse, un intérêt particulier est porté aux systèmes {FeCo} en raison de leur capacité à présenter une bistabilité électronique (propriétés photomagnétiques ou de molécules/chaines aimants). Les systèmes cyanuré {FeCo} sont particulièrement adaptés pour l'observation de réarrangements électroniques thermo- et/ou photo-induit, comme en témoignent le nombre important de composés cyanurés photomagnétiques dans la littérature. / The work presented in this PhD dissertation focuses on the synthesis and the characterisation of octahedral iron(II) and iron(III) complexes coordinated by a tridentate ligand of the scorpionate family (fac- geometry) and three cyanide ligands. Their use as metalloligands in respect to partially blocked metal ions is studied. Because of their ambidentate character, cyanide ligands open the door to facile synthesis of heterobimetallic species. Moreover, these ligands are known to be efficient magnetic exchange interaction transmitter, thus favouring intramolecular electronic communication between the metal ions they are bridging. The functionalisation of scorpionate ligands allows control over the intrinsic electronic properties of the iron precursor complexes, thus allows to tune the properties of the obtained polynuclear species from the latter by self-assembly. In this PhD dissertation, a particular interest was taken in {FeCo} systems because of their potential ability to exhibit electronic bistability (photomagnetic properties or SMM/SCM behaviour). Cyanide-bridged {FeCo} systems are particularly suitable for the observation of thermally or light-induced electron rearrangements, as testified by the wide range of photomagnetic cyanide-bridged compounds in the literature.

<p>A series of uranium benzyl compounds supported by two hydrotris(3,5-dimethylpyrazolyl) borate (Tp*) ligands has been synthesized and characterized. In addition to the previously reported Tp*₂U(CH₂Ph) (<b>2-Bn</b>), examinations of both steric (<i>tert</i>-butyl, <i>iso</i>-propyl) and electronic (methoxy, picolyl) changes on the aromatic ring led to the formula Tp*₂U(CH₂Ar) (Ar = 4-<i>tert</i>-butylphenyl (<b>2-<i>^t</i>Bu</b>), 4-isopropyl (<b>2-ⁱPr</b>), 2-picolyl (<b>2-pyr</b>), 3-methoxyphenyl (<b>2-OMe</b>). Treatment of the entire series of benzyl compounds with azidotrimethylsilane results in the formation of a neutral, monomeric U(III) compound, Tp*₂U(N₃) (<b>3-N₃</b>), and substituted benzyltrimethylsilane. While there was no observed change in reactivity among the benzyl compounds and Me₃SiN₃, treatment of these compounds with triphenylphosphine oxide saw unique carbon-carbon coupling occur for three of the substituted benzyl compounds. With a single equivalent of OPPh₃, the following products were isolated: Tp*₂U[OP(C₆H₅)(C₆H₅CH₂C₆H₅)] (<b>4-Ph</b>), Tp*₂U[OP(C₆H₅)(C₆H₅-<i>p</i>-<i>i</i>PrC₆H₄)] (<b>4-ⁱPr</b>), Tp*₂U[OP(C₆H₅)(C₆H₅-<i>p</i>-<i>t</i>BuC₆H₄)] (<b>4-<i>^t</i>Bu</b>), Tp*₂U[OP(C₆H₅)(C₆H₅-<i>m</i>-OCH₃C₆H₄)] (<b>4-OMe</b>). </p> <p> A family of uranium(IV) imido complexes of the form Tp*₂U(NR) (R = benzyl (<b>7-Bn</b>), <i>para</i>-tolyl (<b>7-Tol</b>), <i>para</i>-methoxyphenyl (<b>7-OMe</b>), 2,6-diethylphenyl (<b>7-detp</b>), 2,6-diisopropylphenyl (<b>7-dipp</b>)) have been generated by bibenzyl extrusion from <b>2-Bn</b>. When <b>7-Bn</b> and <b>7-Tol</b>, along with previously reported Tp*₂U(N-Ph) (<b>7-Ph</b>) and Tp*₂U(N-Ad) (<b>7-Ad</b>), are treated with isocyanates or isothiocyanates, they readily undergo [2π+2π]-cycloaddition to generate κ²-ureato and κ²-thioureato derivatives, respectively. Use of phenylisoselenocyanate with <b>7-Tol</b> and <b>7-Ph</b> generates a rare κ²-selenoureato complex. Treating <b>7-Tol</b> and <b>7-OMe</b> with benzonitrile or 4-cyanopryidine results in unusual products of multiple bond metathesis, namely κ¹-amidinate U(IV) complexes. </p> <p>A family of dinuclear bis(Tp*) (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) uranium compounds with conjugated organic linkers was synthesized to explore possible electronic communication between uranium ions. Trivalent diuranium phenyl alkynyl compounds, Tp*₂UCC(1,3-C₆H₄)CCUTp*₂ (<b>14-<i>meta</i></b>) or Tp*₂UCC(1,4-C₆H₄)CCUTp*₂ (<b>14-<i>para</i></b>), and tetravalent diuranium phenylimido compounds, Tp*₂U(N-1,3-C₆H₄-N)UTp*₂ (<b>15-<i>meta</i></b>) and Tp*₂U(N-1,4-C₆H₄-N)UTp*₂ (<b>15-<i>para</i></b>), were generated from trivalent Tp*₂UCH₂Ph. All compounds were fully characterized both spectroscopically and structurally. The electronic structures of all derivatives were interrogated using magnetic measurements, electrochemistry, and were the subject of computational analyses. All of this data combined established that little electronic communication exists between the uranium centers in these trivalent and tetravalent diuranium molecules.</p> <p>Uranium mono(imido) species have been prepared via oxidation of Cp*U(^MesPDI^Me)(THF) (<b>16-Cp</b>*) and [Cp^PU(^MesPDI^Me)]₂ (<b>16-Cp^P</b>) (Cp* = <i>η</i>⁵-1,2,3,4,5-pentamethylcyclopentadienide; Cp^P = 1-(7,7-dimethylbenzyl)cyclopentadienide; ^MesPDI^Me = 2,6-((Mes)N=CMe)₂C₅H₃N, Mes = 2,4,6-trimethylphenyl) with organoazides. Treating either with N₃DIPP formed uranium(IV) mono(imido) complexes, Cp^PU(NDIPP)(^MesPDI^Me) (<b>17-Cp^P</b>) and Cp*U(NDIPP)(^MesPDI^Me) (<b>17-Cp*</b>), featuring reduced [^MesPDI^Me]^1-. Addition of electron-donating 1-azidoadamantane (N₃Ad) to <b>16-Cp*</b> generated a dimeric product, [Cp*U(NAd)(^MesHPDI^Me)]₂ (<b>18</b>), from radical coupling at the <i>para</i>-pyridine position of the pyridine(diimine) ligand and H-atom abstraction, formed through a monomeric intermediate that was observed in solution but could not be isolated. To support this, Cp*U(<i>^t</i>Bu-^MesPDI^Me)(THF) (<b>16-<i>^t</i>Bu</b>), which has a <i>tert</i>-butyl group protecting the <i>para</i>-position, was also treated with N₃Ad, and the monomeric product, Cp*U(NAd)(<i>^t</i>Bu-^MesPDI^Me) (<b>17-<i>^t</i>Bu</b>), was isolated. All isolated complexes were analyzed spectroscopically and structurally, and dynamic solution behavior was examined using electronic absorption spectroscopy. </p>

No description available.

No description available.

No description available.

Scorpionate and terpyridine ligands are of importance in inorganic chemistry for their metal-binding properties. Tris-pyrazolylborate (Scorpionate) ligands that show facial binding mode and steric protection have been extensively used to synthesize complexes modeling the active site structure and biological function of various metalloproteins and as catalysts in C-H and NO activation and carbine transfer reactions. Terpyridine and modified terpyridine ligands showing meridional binding mode have been used in bioinorganic chemistry where Pt-terpyridine complexes are known to inhibit the activity of thiordoxin reductase (TrxR) besides showing interaction with G-quadruplex. The thesis work stems from our interest to use these ligand systems to design and prepare new 3-d metal-based photodynamic therapeutic (PDT) agents to explore their visible light-induced DNA cleavage activity and photocytotoxicity. Efforts have been made in this thesis work to design and synthesize Co(II) and Cu(II) complexes having scorpionate (Tpph) abd terpyridine (tpy) ligands. Ternary 3d-metal complexes having Tpph and planar phenanthroline bases have been synthesized and structurally characterized. The steric encumbrance of Tpph has led to the reduction in chemical nuclease activity along with enhanced photo-induced DNA cleavage activity, particularly of the Cu(II) and Co(II) complexes. The Co(II), Cu(II) and Zn(II) complexes of Tpph and a pyridyl ligand having a photoactive naphthalilmide moiety show molecular light-switch effect on binding to calf thymus DNA or BSA protein. The complexes do not show any chemical nuclease activity. The Cu(II) complex shows significant DNA cleavage activity in red light. The Co(II) complex displays significant photocytotoxicity in UV-A light. Ternary Cu(II) complexes of ph-tpy and heterocycylic bases are prepared and their DNA binding and cleavage activity studied. The complexes are avid binders to CT-DNA. The dipyridoquinoxaline (dpq) and dipyridophenazine (dppz) complexes are photocleavers of DNA in visible light. A significant enhancement in cytotoxicity in HeLa cancer cells is observed on exposure of the dppz complex to light. The binary Cu(II) complexes are also prepared to reduce the dark toxicity using phenyl and pyrenyl substituted terpyridine ligands. The pyrenyl substituted complex shows DNA cleavage activity in the visible light, low dark toxicity and unprecedented photocytotoxicity in visible light. The copper(II) complexes generally show dark cellular toxicity due to the presence of reducing thiols. The present terpyridine copper(II) complex having pendant pyrenyl moiety shows significant PDT effect that is similar to that of the PDT drug Photofrin. Binary Co(II) complexes show efficient DNA cleavage activity in visible light, significant photocytotoxicity in visible light and cytosolic uptake behaviour. Considering the bio-essential nature of the cobalt and copper ions, the present study opens up new strategies for designing and developing 3d-metal-based photosensitizers for their potential applications in PDT.

No description available.