Degree Discipline

Synthesis, Characterization and Catalytic Studies of Chiral Gold Acyclic Diaminocarbene Complexes (open access)

Synthesis, Characterization and Catalytic Studies of Chiral Gold Acyclic Diaminocarbene Complexes

Chiral gold complexes have been applied in homogeneous catalytic reactions since 1986, in some cases with high enantioselectivity. Acyclic diaminocarbene (ADC) ligands are acyclic analogues of N-heterocyclic carbenes (NHCs) that have larger N-CCarbene-N angles and stronger donating ability. ADCs have been developed as alternatives to phosphine and NHC ligands in homogeneous gold catalysis. In 2012, a new series of chiral gold(I) ADCs were first developed by Slaughter's group and were shown to give remarkable enantioselectivities in some reactions. Because of the hindered rotation of the N-CCarbene bonds of ADC, chiral ADC substituents can easily get close to the metal center in some conformations, although two rotameric structures are formed if the chiral amine is nonsymmetric. The selective of specific ADC conformations was the initial focus of this study. Formational selectivity of one diastereomer of an ADC ligand during synthesis was examines by measuring the relative rates of diastereomer formation in a 1H NMR kinetic study. The potential for converting multiple conformational isomers of ADCs into a single conformation, or at least a simpler mixture, was examined. This study used the analogy that anti- isomer has electronic and structural similarity with urea/thiourea, raising the possibility that 1,8-naphthyridine can be used to …
Date: August 2016
Creator: Zhang, Xiaofan
System: The UNT Digital Library
Exploring Inorganic Catalysis with Electronic Structure Simulations (open access)

Exploring Inorganic Catalysis with Electronic Structure Simulations

Organometallic catalysis has attracted significant interest from both industry and academia due to its wide applications in organic synthetic transformations. Example of such transformations include the reaction of a zinc carbenoid with olefins to form cyclopropanes. The first project is a computational study using both density functional and correlated wavefunction methods of the reaction between ethylene and model zinc carbenoid, nitrenoid and oxenoid complexes (L-Zn-E-X, E = CH2, NH or O, L = X = I or Cl). It was shown that cyclopropanation of ethylene with IZnCH2I and aziridination of ethylene with IZnNHI proceed via a single-step mechanism with an asynchronous transition state. The reaction barrier for the aziridination with IZnNHI is lower than that of cyclopropanation. Changing the leaving group of IZnNHI from I to Cl, changes the mechanism of the aziridination reaction to a two-step pathway. The calculation results from the epoxidation with IZnOI and ClZnOCl oxenoids suggest a two-step mechanism for both oxenoids. Another important example of organometallic catalysis is the formation of alkyl arenes from arenes and olefins using transition metal catalysis (olefin hydroarylation). We studied with DFT methods the mechanism of a novel Rh catalyst (FlDAB)Rh(TFA)(η2–C2H4) [FlDAB = N,N’ -bis(pentafluorophenyl)-2,3-dimethyl-1,4-diaza-1,3-butadiene; TFA = trifluoroacetate] that converts …
Date: May 2016
Creator: Khani, Sarah Karbalaei
System: The UNT Digital Library