This thesis describes the study of a series of platinum complexes, with particular emphasis towards hydrosilation. Platinum bis(phosphine) azodicarbonyl complexes Pt(PRI 3)2(R20CNNCOR2) (RI = Ph, Me; R2 = Ph, Me, OEt, Pri) were synthesised and studied. Multinuclear NMR spectroscopy on Pt(PRI3)2(R20CNNCOR2) revealed that the dicarbonyl substituted azo ligand is co-ordinated asymmetrically, consistent with a five membered, Pt-N-N-C-O ring. The crystal structure of Pt(PPh3)2(Pri02CNNC02Pri) shows that the co-ordination sphere of platinum is essentially square planar and co-planar with the five-membered, Pt(1)-0(1)-C(5)-N(2)-N(1) ring. The Pt(PRI 3)lR20CNNCOR2) complexes show sensitivity towards chlorinated solvents (CH2CI2, CHCI3) under photolysis conditions forming the corresponding platinum bis(phosphine) dichloride complexes; the same products are formed in a slower thermal reaction but only for complexes with azodicarboxylate ligands. Complexes with azodicarboxylate ligands also react photochemically with ethylene in ds-THF yielding Pt(PPh3)2(C2H4) but the azodiacyl analogues are inert in this respect. Azodicarboxylate compounds R02CNNC02R (R = Et, Pri, But) are inhibitors of the catalytic activity of [(Pt {174 _(CH2=CHSiMe2hO }h {.u-( CH2=CHSiMe2)20}] for the hydrosilation reaction. The inhibited species can be decomposed thermally or photoch~mically to give active hydrosilation catalysts. It was found that the bulky azo compound But02CNNC02But was the least effective inhibitor of [(Pt{ 174 - '(CH2=CHSiMe2hO} )2(P-( CH2=CHSiMe2)20)]. The photochemistry of platinum bis(phosphine) malonates and phthalates was found to be limited, and their reactivities were much lower compared to the analogous oxalate complexes. Silyl hydride complexes, cis-Pt(PCY3)2(H)(SiR3), were synthesised from the reaction of Pt(PCY3)2 and the corresponding silane. These complexes were undergo dynamic exchange in solution. Two exchange processes were identified; the first involves mutual phosphine exchange, i.e. positional interchange between the hydride and the silyl ligands. The second process occurs at higher temperatures (above 290 K) and involves the elimination and re-addition of the silane ligand HSiR3. Thermodynamic and activation parameters are obtained for cis-Pt(PCY3)2(SiR3) (R = Ph, SiR3 = SiMe2CH2CH=CH2, SiMe2Et). The reaction of Pt(PCY3)2 with the disilane HSiMe2(l,2-C6~)SiMe2H is thought to form a Pt(IV) bis(silyl) dihydride trigonal bipyramidal species of the form, Pt(PCY3)(H)2[SiMe2(1,2-C6~)SiMe2]' where the hydride ligands are in the axial positions. All of the platinum silyl hydride complexes studied degrade thermally to form trans-Pt(PCY3)2(H)2 at, or above, room temperature.

No description available.

Abstract This thesis is a summary of five papers, containing equilibrium and structure studies of aqueous molybdate and peroxomolybdate species. Some of the peroxomolybdate species have also been studied in terms of their dynamic and catalytic properties. The primary objective was to characterize species with potential catalytic activity, with emphasis on thebleach process of kraft pulp. For this, potentiometry, EXAFS and 17O, 31P, 1H and 95 Mo NMR have been used. The molybdate speciation in 0.300 M Na2(SO4) medium was found to differ from that in 0.600 M Na(Cl) medium, in that the uncharged monomeric molybdate species H2MoO4 was stronger in the sulphate medium, while highly charged species, such as Mo7O24 6-, became somewhat less pronounced. Diperoxomolybdate species, (MoX2)n (X = peroxo ligand, n = 1-2), dominated the peroxomolybdate systems when sufficient peroxide was available. Both sulphate and chloride coordinated to molybdenum in the presence of hydrogen peroxide and these species were more inert than diperoxomolybdate species without coordinated medium anions. Chemical exchange rates increased upon protonation. A dimeric triperoxomolydate species was the only species found that contained more than two peroxo groups per molybdenum atom. At low concentrations of hydrogen peroxide, monoperoxoheptamolybdate species, Mo7X, were found. Phosphate was found to coordinate relatively weakly to molybdate in the presence of peroxide. Species with four different nuclearities, i.e. (MoX2)nP (n = 1-4), were found. At excess of peroxide, no molybdophosphates were present. Chemical exchange rates were found to be substantially lower than in the peroxomolybdate system. The aqueous monomeric diperoxomolybdate species retain the pentagonal bipyramidal seven-coordination found in the solid state, although with increased bond lengths. Sulphate seems to coordinate to molybdenum in a monodentate fashion by replacing an oxygen atom. Chloride probably coordinates by replacing an oxygen atom as well. For the dimeric diperoxomolybdate species, a single oxygen-bridge was proposed. Conjugated carbon double bonds in the side chains of lignin model compounds were found to be hydroxylated or epoxidised by peroxomolybdate species. The addition of phosphate did not affect the type or yield of oxidation products noticeably. It was also shown that hydrogen peroxide, in the absence of molybdate, did not react to any noticeable extent with the lignin model compounds under these conditions.

Mono- and dinuclear chromiumtricarbonyl and manganesetricarbonyl complexes of dibenzo[a,e]cyclooctatetraene (DBCOT) were synthesized and characterized. In the bis(chromiumtricarbonyl)DBCOT synthesis, the main product was the syn,anti isomer where the two Cr(CO)3 moieties coordinate to opposite faces of the DBCOT backbone. This complex exhibits three dynamic processes in solution. A ring inversion of the organic skeleton occurs while the two chromiumtricarbonyl moieties undergo tripod rotation. This is the first study where eight-membered ring inversion is studied for a pi-coordinated metallic system. The rate of inversion at various temperatures was determined by 1H NMR line shape analysis at two different field strengths (300 and 600 MHz). Compared with other cyclooctatetraene compounds reported, there is a large positive entropy of activation and a relatively high enthalpy of activation in this system. DFT calculations, using the B3LYP/6-31G** basis set, were performed to gain a better understanding of the experimental results. It is proposed that free rotation of both Cr(CO)3 groups in the planar transition state are responsible for the large entropy of activation for ring inversion in hexahapto,hexahapto-dibenzo[a,e]cyclooctatetraene-syn,anti-bis(tricarbonylchromium). The relatively large enthalpy of activation is due to a stabilizing interaction between the endo carbonyl groups on the syn-Cr(CO)3 and the remote arene. In the monometallic DBCOT complexes, the metal can either be inside or outside the tub conformation. Interestingly, the crystal structures show opposite orientations for the isoelectronic chromium and manganese systems. The Cr(CO)3 group is positioned anti relative to the DBCOT backbone while the Mn(CO)3+ is syn. It should be noted that the optimized gas phase geometries obtained through DFT calculations agree with the crystallographic results. Electrochemical studies were performed to investigate the change in redox behavior associated with coordination of mono and bis-chromium units to the DBCOT backbone. Four new organometallic crystal structures are reported in this dissertation. Different tripod orientations, DBCOT backbone angles, and metal orientation relative to the interior of the organic skeleton are found. C-H...O, C-H...pi, and charge assisted C-H...F hydrogen bonding interactions were observed in the solid state packing. The structural motifs found suggest these complexes could serve as organometallic synthons in supramolecular chemistry.

Le cannabidiol (CBD), constituant majeur non-psychotrope du Cannabis sativa, possède un grand nombre de propriétés pharmacologiques. Des dérivés du CBD présentant une rotation restreinte autour de la liaison simple aryl-C(sp3) ont été synthétisés avec deux modifications majeures apportés sur l’un ou/et l’autre cycle dans le but d’atteindre et de contrôler l’atropisomérie.Des phénylcyclohexanes diversement substitués ont été préparés par hydrogénation catalytique des phénylcyclohexènes correspondants. Des études de RMN dynamique et de modélisation moléculaire ont permis l’identification des épimères (1R/1S) et de leurs conformères (M/P). Selon la nature des substituants, de bons résultats de diastéréosélectivité et d’atroposélectivité ont été obtenus. Les conformères de l’épimère (1S) ont des barrières de rotation élevées jusqu’à 92 kJ.mol-1, contrairement à ceux de (1R) avec des barrières de seulement ~72 kJ.mol-1. L’atropisomérie dépend non seulement des substituants autour l’axe de chiralité mais aussi de la position d’un groupe méthyle sur le cycle monoterpénique (en C1).Des dérivés ortho-soufrés ont été préparés à partir de leurs analogues oxygénés via le réarrangement de Newman-Kwart. La substitution de l’atome d’oxygène par le soufre ralentit significativement l’échange conformationnel, les barrières énergétiques augmentent d’environ 10 kJ.mol-1. / Cannabidiol (CBD) is the major non-psychoactive constituent of Cannabis sativa with a large number of pharmaceutical interests. CBD derivatives with restricted rotation about the aryl-C(sp3) single bond have been synthesized with two major changes on one and/or both cycles in order to reach and control atropisomerism.Diversely substituted phenylcyclohexanes were prepared by catalytic hydrogenation from their corresponding phenylcyclohexenes. Dynamic NMR experiments and DFT calculations allowed us to identify the epimers (1R/1S) and their conformers (M/P). According to the nature of the substituents, high diastereoselectiviy and atrop-selectivity were obtained in these natural product derivatives. The conformers of epimers (1S) show high rotational barriers of up to 92 kJ.mol-1, unlike those of (1R) and with much lower barriers of ~72 kJ.mol-1. Atropisomerism not only depends on the substituents at the axis of chirality but also is influenced by the position of a methyl group on the monterpene ring (at C1).Ortho-thio derivatives were prepared from their oxygenated analogs via the Newman-Kwart rearrangement. The substitution of the oxygen atom by the sulfur slows the conformational exchange significantly increasing the rotational barriers of around 10 kJ.mol-1.

The main objective of this project is to synthesize the first family of polynuclear chromium pyrazolate complexes. Complexity in analysis of the experimental magnetic data of multinuclear complexes arises from their (2S +1)N microstates, where S is the spin of each metal center and N is the number of metal centers. For example, high-spin (HS)-FeIII3 has 216 microstates and HS-FeIII8 ≈ 1.7x106 microstates (S= 5/2). However, complexes with chromium(III) S = 3/2 will have a noticeable reduction of microstates. Mononuclear complexes with formula [mer-CrCl3(pzH*)3] (pz*H = pyrazole, 3-Me-pzH, 4-Me-pzH, 4-Cl-pzH, 4-I-pzH, 4-Br-pzH) and [trans-CrCl2(pzH*)4]Cl (pzH* = pyrazole and 3-Me-pzH) were synthesized and thoroughly characterized. Polynuclear iron pyrazolate complexes are prepared by the addition of base to [mer-FeCl3(pzH*)3] and [trans-FeCl2(pzH*)4]Cl complexes; the path is not paralleled by mononuclear chromium(III) pyrazole complexes. There is a challenging situation with these reactions, caused by the attainment of equilibrium, where the stable mononuclear complexes and traces of dinuclear species coexist in solution. Microwave assisted reaction of Cr(NO3)3·9H2O and pyrazole ligand in dimethylformamide (DMF) solution afforded redox inactive trinuclear formate-pyrazolate mixed-ligand complexes with formula [Cr3(μ3-O)(μ-O2CH)3(μ-4-R-pz)3(DMF)3]+ (pz = pyrazolate anion; R= H, Me, Cl). Thermally assisted synthesis with non-hydrolysable solvent yielded an electrochemically active all-pyrazolate complex. Complex with formula (Ph4P)2[Cr3(μ3-O)(μ-4-Cl-pz)6Cl3] and (Ph4P)2[Cr3(μ3-O)(μ-4-Cl-pz)6Br3] have an oxidation process at 0.502 V at 0.332 V, respectively. The latter has a second accessed oxidation process at 0.584 V. These systems are the first example of electrochemically amendable trinuclear pyrazolate complex with {Cr3O} core. The all-ferric complexes [Fe3(μ3-O)(μ-4-NO2-pz)6(L)3]2- (L = NCO-, N3) were synthesized from reaction of [Fe3(μ3-O)(μ-4-NO2-pz)6Cl3]2- with NaNCO and NaN3. Expected reversible reduction processes were observed for both complexes at more negative potential, -0.70 V, compared to the thiocyanate complex (-0.36 V). The 57Fe Mössbauer of the reduced [Fe3(μ3-O)(μ-4-NO2-pz)6(N3)3]3- is suggestive of a HS-to-LS electronic reorganization, as seen for the [Fe3(μ3-O)(μ-4-NO2-pz)6(SCN)3]3- complex. Furthermore, compound [Fe3(μ3-O)(μ-4-NO2-pz)6(N3)3]2-, shows a unique reversible oxidation process at 0.82 V (vs. Fc+/Fc) to a mixed-valent, formally Fe3+2/Fe4+ species.

No description available.

Cationâ Ï interaction is an important determinant in protein structure and function. Among the three proteinogenic aromatic amino acids, tryptophan (Trp) is the strongest cationâ Ï donor. We reported the asymmetric syntheses of tryptophan regioisomers in which the amino acid side chain is attached at different position of the indole moiety. These new tryptophan regioisomers can effect a different mode of cationâ Ï interaction. In nature, dramatic increases in binding affinity can be achieved through multivalent binding. Following a fragmentation-dimerization approach, we synthesized Taxol-based dimer in which the baccatin III core of Taxol is coupled with flexible PEG linker. However, microtubule assembly assay suggested that these new dimers are not capable of effecting bivalent binding to the Taxol binding sites in microtubules. Memory of chirality (MOC) is an emerging theme in asymmetric synthesis in which the dynamic chirality of the reactive intermediate "memorizes" the static chirality of the reactant. Using dynamic 1D and 2D NMR and density functional theory (DFT) methods, we studied the MOC effect of 1,4-benzodiazepin-2-ones. Reconstruction of the reaction pathway using DFT calculations supported our proposed contra steric, retention of configuration mechanism. / Ph. D.