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No description available.

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Laccase (E.C 1.10.3.2) catalyzes the oxidation of aromatic substrates with the simultaneous reduction of molecular oxygen to water. It has significant potential for use in many applications due to its high reaction rates, broad substrate-specificity, and use of oxygen as an inexpensive co-factor. The objective of this research was to investigate the ability of laccase from Trametes versicolor to catalyze oxidation reactions under a variety of reaction conditions and to model the kinetics of these transformations. Phenol was selected as a model substrate. / Laccase was very stable when incubated at temperatures less than 30°C and pHs between 6 and 7. The optimum pH for phenol transformation was 6, but when present in sufficient quantities, laccase was able to significantly transform phenol at pHs from 4 to 7 and temperatures from 10 to 60°C. Laccase stability was negatively impacted by the presence of four common redox mediators. Of these, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonate) (ABTS) and 2,2',6,6'-tetramethylpiperidine-N-oxyl (TEMPO) significantly enhanced phenol transformation but large quantities were required, which may limit the feasibility of the use of these mediators in many applications. / A series of kinetic models was developed in order to achieve a better understanding of the mechanisms and kinetics of laccase-catalyzed reactions and to eventually assist in the choice and design of suitable reactor systems. These models were designed to predict the transient oxygen and phenol concentrations during laccasecatalyzed reactions at pH 6 and 25°C. Over the course of developing and validating these models, it was observed that: (1) the rate-limiting step in the catalytic reactions is the reaction between the oxidized form of laccase and phenol; (2) the stoichiometric ratio, which is defined as the molar ratio of phenol transformed to oxygen consumed in the catalytic reaction, was found to increase with phenol concentration in the reaction mixture from a theoretical lower limit of 1 and to approach a theoretical upper limit of 4; and (3) laccase inactivation occurs over the course of the reaction and was found to be dependent on the rate of substrate transformation. / Ultimately, these findings were incorporated into a comprehensive kinetic model to predict transient species concentrations in an open-system environment where the degree of substrate transformation was not limited by oxygen availability. The model accounts for enzyme kinetics, oxygen mass-transfer, variable reaction stoichiometry, and inactivation related to reaction products. Excellent agreement was observed between measured and modeled phenol and oxygen concentrations for a wide range of initial phenol concentrations and enzyme activities. Simplified models were also developed by incorporating an assumption, referred to as the pseudo-steady-state assumption, that at any instant during the reaction, the enzyme achieves an approximate steady-state distribution of its various forms around the catalytic cycle. The pseudo-steady-state assumption had the advantage of reducing the complexity of model equations without sacrificing their predictive abilities and allowing enzyme quantities to be expressed in activity units instead of molar concentrations.

Bis(amidinate) dichloride complexes of the type M(L)2Cl2 (M=Zr, 2a; M=Ti, 2b; L=CyNC(C5H5FeC5H4)NCy) were synthesized by treating 2 equiv of ferrocenyl amidine, H(L), with M(NMe2)2Cl2 (M=Ti, Zr.2THF). Half sandwich mono(amidinate) complexes, Cp’ZrLCl2 (Cp’=Cp, 2c; Cp’=Cp*, 2d), were prepared by the reaction of Cp’ZrCl3 with 1 equiv of Li(L). The dialkyl complexes, M(L)2Me2 (M=Zr, 3a; M=Ti, 3b), CpZr(L)(CH2Ph)2 (3c) and Cp*Zr(L)Me2 (3d) were prepared by treatment of the dichloride complexes (2a-2d) with an appropriate alkylating agent. The dichloride complexes (2a-2d) activated with MAO, and dialkyl complexes (3a-3d) activated with B(C6F5)3 and [Ph3C][B(C6F5)4] show low to moderate ethylene polymerization activities. Cyclic voltammetry studies on the metal complexes containing ferrocenyl amidinates reveals quasi reversible oxidation and reduction waves for the ferrocene/ferrocenium couple.

Bis(amidinate) dichloride complexes of the type M(L)2Cl2 (M=Zr, 2a; M=Ti, 2b; L=CyNC(C5H5FeC5H4)NCy) were synthesized by treating 2 equiv of ferrocenyl amidine, H(L), with M(NMe2)2Cl2 (M=Ti, Zr.2THF). Half sandwich mono(amidinate) complexes, Cp’ZrLCl2 (Cp’=Cp, 2c; Cp’=Cp*, 2d), were prepared by the reaction of Cp’ZrCl3 with 1 equiv of Li(L). The dialkyl complexes, M(L)2Me2 (M=Zr, 3a; M=Ti, 3b), CpZr(L)(CH2Ph)2 (3c) and Cp*Zr(L)Me2 (3d) were prepared by treatment of the dichloride complexes (2a-2d) with an appropriate alkylating agent. The dichloride complexes (2a-2d) activated with MAO, and dialkyl complexes (3a-3d) activated with B(C6F5)3 and [Ph3C][B(C6F5)4] show low to moderate ethylene polymerization activities. Cyclic voltammetry studies on the metal complexes containing ferrocenyl amidinates reveals quasi reversible oxidation and reduction waves for the ferrocene/ferrocenium couple.

In the pursuit of increasingly efficient and/or new chemical transformations, homogeneous transition metal catalysts are proving to be invaluable components of the synthetic chemist’s toolbox. Notwithstanding the many important contributions made to the area of synthetic chemistry utilizing other transition metal catalysts, palladium-catalyzed cross-coupling techniques have been demonstrated to allow for a plethora of otherwise very difficult or even impossible bond forming reactions to be realized. In this context, appropriately designed ancillary ligands, which upon binding to a metal center can influence metal-centred reactivity, have played an essential role in the advancement of palladium-catalyzed cross-coupling reactions. This thesis describes a multi-faceted approach to the identification of effective ligands for the palladium-catalyzed construction of (sp2)carbon-nitrogen and -oxygen bonds. A new series of P,O-DalPhos ligands were developed and applied in the synthesis of of N-substituted indoles via tandem palladium-catalyzed cross-coupling/cyclizations of ortho-alkynylhalo(hetero)arenes with primary amines. Notably, one P,O-DalPhos variant, OTips-DalPhos, was demonstrated to offer the broadest known substrate scope in this important class of transformations, affording a variety of structurally diverse indoles and related heterocyclic derivatives in high yields. Also described herein is the identification of the previously reported ligand BippyPhos as an extremely robust and versatile ligand in both palladium-catalyzed carbon-nitrogen and -oxygen cross-coupling applications. Indeed, the use of a Pd/BippyPhos catalyst enabled the cross-coupling of a range of (hetero)aryl (pseudo)halides with primary and secondary amines, NH heterocycles, amides, ammonia and hydrazine, with representative examples being accommodated in air. The unprecedented scope of the Pd/BippyPhos catalyst in carbon-nitrogen cross-coupling allowed for the development of two novel one-pot, two-step syntheses of N¬-aryl heterocycles from ammonia, ortho-alkynylhalo(hetero)arenes and (hetero)aryl halides through tandem N-arylation/hydroamination reactions. A marked selectivity profile was also observed for the Pd/BippyPhos catalyst and successfully exploited in the chemoselective monoarylation of substrates featuring two distinct and potentially reactive NH-containing moieties. Finally, Pd/BippyPhos mixtures served as robust and efficient catalysts for the hydroxylation of a range of (hetero)aryl halides and ortho-alkynyl(halo)heteroarenes to form phenols and phenol-derived heterocycles.

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