A kinetic study of the reactions of Group VI-B hexacarbonyls with primary amine and halide ligands was undertaken in order to determine the possible mechanisms of these reactions. As well as the expected dissociative pathway, the reactions with the primary amines were seen to proceed by a concurrent pathway which was dependent upon the ligand concentration. Since nitrogen donor ligands are expected to be poor donor ligands, the mechanism proposed was a "dissociative interchange" mechanism which should not be too dependent upon the nucleophilicity of the ligand. Comparison of the rate constants for the amines studied as well as those of the previously investigated Lewis base ligands indicated all such reactions may proceed through the same mechanism. The similarity in rate constants for the ligand-independent and ligand-dependent pathways supports this mechanism. The rate of formation of the final product was seen to be dependent upon the square of the mercuric halide concentration. Therefore, the conversion of Fe(CO)4(HgX)2 to the final product was proposed to proceed by the successive abstraction by each HgX group of two molecules of mercuric halide. These oxidative elimination reactions are related to a chemical model for the intermediate step in the reduction of dinitrogen to ammonia and their similarities and differences are discussed.

Electronic and steric parameters for square planar NiN2S2 complexes as bidentate, S-donor ligands have been established. According to the (CO) stretching frequencies and associated computed Cotton-Kraihanzel force constants of (NiN2S2)W(CO)4 adducts, a ranking of donor abilities and a comparison with classical bidentate ligands are as follows: Ni(ema)= > { [NiN2S2]0 } > bipy phen > Ph2PCH2CH2PPh2 > Ph2PCH2PPh2. In addition, we have demonstrated that the NiN2S2 ligands are hemilabile as evidenced from CO addition to (NiN2S2)W(CO)4, which is in equilibrium with the resulting (NiN2S2)W(CO)5 species (Keq = 2.8 M-1, G = -1.4 kJ/mole at 50C). Complete NiN2S2 ligand displacement by CO-cleavage of the remaining W-S bond to form W(CO)6 was not observed, indicating that the remaining W-S bond is considerably strengthened upon ring-opening. Several new cluster compounds based on the NiN2S2 ligands bound to CuI, RhI, PdII and W0 are reported. Structural analysis of (NiN2S2)MLn complexes show a unique structural feature defined by the dihedral angle formed by the intersection of NiN2S2/WS2C2 planes; placing the NiN2S2 ligand in closer proximity to one side of the reactive metal center. This unique orientational feature of the NiN2S2 ligands in the series of bimetallic compounds contrasts with classical diphosphine or diimine ligands. The "hinge angle" ranges in value from 136 as in the (Ni-1*)W(CO)4 to 101 in the (Ni-1)Pd(CH3)(Cl) complexes. The rigidity of the SR hinge of the nickeldithiolate ligands suggests that they might be suitable for stereochemical and regioselective substrate addition to catalytically active metals such as RhI and PdII.. The structural as well as functional similarities of the acetyl CoA synthase enzyme (ACS) and a palladium-metal based industrial type catalyst led to the preparation of a [(Ni-1)Pd(CH3)]+ bimetallic complex. This complex facilitates CO and ethylene copolymerization to produce polyketone similar to conventional (diphosphine)Pd(X)2 catalysts. However, the diphosphine ligands produce more efficient catalysts as the electron-rich character of the NiN2S2 ligand favors the resting state of the catalyst, [(Ni-1)Pd(C(O)CH3)(CO)]+, over the reactive form (Ni-1)Pd(C(O)CH3)(2-C2H4)]+. An exploratory investigation with the Ni-Pd heterobimetallic showed that this complex also facilitated the C-S coupling reaction to form a thioester similar to the ACS enzyme.

Electronic and steric parameters for square planar NiN2S2 complexes as bidentate, S-donor ligands have been established. According to the (CO) stretching frequencies and associated computed Cotton-Kraihanzel force constants of (NiN2S2)W(CO)4 adducts, a ranking of donor abilities and a comparison with classical bidentate ligands are as follows: Ni(ema)= > { [NiN2S2]0 } > bipy phen > Ph2PCH2CH2PPh2 > Ph2PCH2PPh2. In addition, we have demonstrated that the NiN2S2 ligands are hemilabile as evidenced from CO addition to (NiN2S2)W(CO)4, which is in equilibrium with the resulting (NiN2S2)W(CO)5 species (Keq = 2.8 M-1, G = -1.4 kJ/mole at 50C). Complete NiN2S2 ligand displacement by CO-cleavage of the remaining W-S bond to form W(CO)6 was not observed, indicating that the remaining W-S bond is considerably strengthened upon ring-opening. Several new cluster compounds based on the NiN2S2 ligands bound to CuI, RhI, PdII and W0 are reported. Structural analysis of (NiN2S2)MLn complexes show a unique structural feature defined by the dihedral angle formed by the intersection of NiN2S2/WS2C2 planes; placing the NiN2S2 ligand in closer proximity to one side of the reactive metal center. This unique orientational feature of the NiN2S2 ligands in the series of bimetallic compounds contrasts with classical diphosphine or diimine ligands. The "hinge angle" ranges in value from 136 as in the (Ni-1*)W(CO)4 to 101 in the (Ni-1)Pd(CH3)(Cl) complexes. The rigidity of the SR hinge of the nickeldithiolate ligands suggests that they might be suitable for stereochemical and regioselective substrate addition to catalytically active metals such as RhI and PdII.. The structural as well as functional similarities of the acetyl CoA synthase enzyme (ACS) and a palladium-metal based industrial type catalyst led to the preparation of a [(Ni-1)Pd(CH3)]+ bimetallic complex. This complex facilitates CO and ethylene copolymerization to produce polyketone similar to conventional (diphosphine)Pd(X)2 catalysts. However, the diphosphine ligands produce more efficient catalysts as the electron-rich character of the NiN2S2 ligand favors the resting state of the catalyst, [(Ni-1)Pd(C(O)CH3)(CO)]+, over the reactive form (Ni-1)Pd(C(O)CH3)(2-C2H4)]+. An exploratory investigation with the Ni-Pd heterobimetallic showed that this complex also facilitated the C-S coupling reaction to form a thioester similar to the ACS enzyme.

Thesis (M. Sc.)--University of Canterbury, 2009. / Typescript (photocopy). "March 2009." Includes bibliographical references (leaves 92-94). Also available via the World Wide Web.

Les quadruplexes de guanines (G4) sont des structures polymorphiques adoptées in vitro par les séquences d’ADN et d’ARN riches en guanines. L’utilisation d’anticorps et de ligands spécifiques des structures G4 a permis leur détection au niveau cellulaire. Des études computationnelles ont prédit des séquences possédant une signature G4 au niveau de régions génomiques capitales comme les télomères ou les promoteurs de certains oncogènes. De plus, de nombreuses protéines impliquées dans des processus cellulaires comme la réplication, la transcription ou encore la réparation, peuvent interagir directement avec des G4, en facilitant leur formation ou au contraire leur dénaturation. C’est notamment le cas d’hélicases impliquées dans des pathologies humaines, comme BLM, WRN, FANC J ou PIF1. Ce sont des enzymes capables de dénaturer des G4 et dont l'inactivation induit une instabilité génomique, en particulier au niveau de régions susceptibles de former un G4. Dans ce travail, nous présentons la mise au point d’un test de criblage à moyen débit pour le suivi des interactions G4/hélicases en temps réel. Ce test nous a permis de définir les conditions favorisant ou inhibant l’interaction d’une hélicase vis-à-vis de son substrat G4. Nous avons démontré que ces conditions pouvaient différer d’une hélicase à une autre, notamment les conditions salines optimales nécessaires aux activités hélicases de ScPif1 et de RHAU. Nous avons également prouvé, à travers ce test, que l’utilisation de ligands capables de stabiliser les G4 n’induisait pas forcément d’inhibition de l’activité hélicase de ScPif1. Enfin, nous avons également pu définir la directionnalité de la protéine RPA, ce qui fait de notre test une technique prometteuse pour la caractérisation de nouvelles protéines pouvant dérouler des structures G4. / G-quadruplexes are highly polymorphic non-canonical nucleic acid structures adopted by both DNA and RNA guanine-rich sequences in vitro. They have been detected at the cellular level using structure specific antibodies and small molecule ligands. Computational studies demonstrated that G4-prone sequences are located in key genomic regions such as telomeres and oncogene promoters. Numerous studies showed that G4 sequences can interact with proteins involved in cellular processes, including replication, transcription or reparation. Those interactions include binding, G4 folding promotion or in contrary unwinding. Indeed, WRN, BLM, FANC J or Pif1 are helicases associated with human-diseases. They can unwind G4 forming sequences; mutation of these helicases lead to genomic instability of G4-prone motifs when mutated. Here, we present a medium-throughput technique to monitor G4-helicase interactions in real time. We were able to determine both favourable and deleterious conditions for G4 unwinding by a given helicase. We show that these conditions differ from one helicase to another as exemplified with the optimal salt conditions required for both ScPif1 and RHAU activities. We also reveal that the G4 ligands that stabilize G4 structures do not necessarily induce an inhibition of their unwinding by ScPif1 helicase. Finally, we also prove that our assay is adapted to clear up RPA directionality, making it an attractive technique to screen for new proteins able to unwind G4 structures.

Ce projet vise la synthèse de différentes familles de ligands pinceurs associant la fonction iminophosphorane (P=N) à d’autres fonctions azotées ou phosphorées. Les ligands pinceurs sont des ligands tridentés, dont la versatilité des structures possibles permet une modulation fine des propriétés électroniques et stériques des complexes formés. L’introduction de fonctions spécifiques permet également d’envisager une coopérativé du ligand.Le premier chapitre décrit la synthèse et la caractérisation de différents complexes ruthénium-hydrure qui différent par la nature des ligands ancillaires. Les complexes obtenus et leurs propriétés ont été comparés à leurs analogues phosphine(s)/amines décrits dans la littérature en particulier pour la catalyse de processus hydrogénants et déshydrogénants. Dans le contexte économique et écologique actuel, la catalyse par des complexes de ruthénium n’apparait pas comme une solution pertinente à long terme. Des complexes de fer analogues ont donc également été développés.Une seconde famille de ligands, différant par la position de la fonction iminophosphorane, a été également synthétisée. Sa coordination à un métal de transition du groupe 11 tel que le cuivre(I) a été étudiée. Les propriétés catalytiques et la réactivité des différents complexes formés ont ensuite été décrites au travers, par exemple, de la réaction d’Huisgen.Enfin, une nouvelle famille de ligands pinceurs triazotés à motif amidoquinoline a ensuite été développée. Sa synthèse est décrite dans ce manuscrit, ainsi que les complexes préparés avec différents métaux du groupe 8 tels que le palladium et le nickel. La réactivité du ligand possédant des substituants phényles avec le nickel(0) a conduit à réarrangement original du ligand. / This research project aims at the synthesis of various types of pincer ligands associating iminophosphorane (P=N) and different nitrogen and phosphorous containing functions. Pincer ligands are tridentate ligands with high degree of synthetic variability allowing a fine tuning of the electronic and steric properties. Cooperativity can also be allowed by introducing specific functions.First chapter deals with the synthesis and characterizations of various ruthenium-hydride complexes which differ by the nature of the ancillary ligands. The obtained complexes and their properties have been compared to their phophine(s)/amine analogues known in the literature, in particular for hydrogenating or dehydrogenating processes. Nevertheless, inthe global economic and ecologic context, ruthenium catalysis does not appear as a sustainable candidate. Therefore iron analogs have also been developed.The modification of the iminophosphorane position led us to synthesize a new family of ligands. Its coordination with a group 11 transition metal such as copper(I) has also been studied. The catalytic properties of those complexes for the Huisgen reaction have also been probed.Finally a new family of pincer ligands containing three coordinating nitrogen atoms with an amidoquinoline moiety has been developed afterwards. Its synthesis is described in this manuscript as well as the complexes formed with group 8 transition metals such as palladium and nickel. An unusual reactivity has been observed when the ligand which includes phenyl substituents on the iminophosphorane reacted with nickel(0).

The chemistry of transition metal clusters has been a fast developing area of organometallic research in recent years. Compared to mononuclear metal complexes, polynuclear clusters offer more opportunities to study cooperative effects and electron reservoir properties between contiguous metal centers, in addition to functioning as storehouses for the release of catalytically active small fragments capable of exhibiting heterosite subtrate activation. Theoretically, metal clusters are intermediates between mononuclear complexes and metal surfaces, i.e., they serve as a bridge between molecular and solid-state chemistry. Transition metal clusters are ideal candidates to study M-M interactions stretching from the single bond to the collective metallic behavior found in a three-dimensional network of metal atoms. The reaction between the redox-active diphoshpine ligand bpcd and RU(CO) has been examined under a variety of conditions. The disubstituted cluster Ru3(CO)10(bpcd)(2) has been synthesized and shown to contain a chealating bpcd ligand, on the basis of IR and 31P NMR data. The cluster 2 (chelating isomer) undergoes cluster fragmentation at ambient temperatures in the dark to give the binuclear compound 3 and Ru3(CO)12, with no evidence for the formation of 4. Both 3 and 4 have been isolated and fully characterized in solution by IR and NMR spectroscopy, and the solid-state structure of each new binuclear compound has been established by X-ray diffraction analysis. Independent experiments reveal that dinuclear 3 is converted to 4 by 366 nm light with a quantum efficiency of .0364.

The class of ligands represented by [CpCo(P(O)(OR)2)3]-, L- , were first synthesized by W. Kläui in 1977. These ligands have been found to coordinate to a variety of low and high oxidation state metals through the use of its three P=O oxygen atoms as donors. The ligands act as mono-anionic six electron donors which make them similar to the more widely known cyclopentadienyl ligands, (C5H5-xRx)-, but have electronic properties like those of fluoride or oxide. Also, it has been found that the coordination chemistry of L- resembles the unsubstituted tris(pryrazolyl)hydroborato six electron ligand, (RB(pz)3)-. All three of these ligands can be modified by changing the substituent R. The Kläui ligand offers a good opportunity to synthesize a chiral derivative. In the process to obtain the chiral version, (cyclopentadienyl)tris(biphenyl-phosphito-P)cobaltate(1-), 18, was synthesized from 2,2'-biphenol. This was characterized through NMR, mass spectroscopy, and XPS. Next, a racemic version, (cyclopentadienyl)tris(biphenylphosphito-P)cobaltate(1-), 17, was synthesized from (±)1,1′-bi-2-naphthol. A one-pot synthesis for the rac-binaphthyl phosphite derivative was developed with an increased yield from the previously published synthesis. The racemic version of the ligand was characterized by NMR and mass spectroscopy. The chiral version has not yet been synthesized, however, by following the developed procedure for the non-chiral version, the ligand could be synthesized from optically active 1,1'-bi-2-naphthol. / Master of Science

No description available.

published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy