Organometallic transformations and living radical polymerizations mediated by group nine metalloporphyrins / Shan Li.

Format:

Book

Manuscript

Microformat

Thesis/Dissertation

Author/Creator:

Li, Shan.

Contributor:

Lester, Marsha I., advisor.

University of Pennsylvania.

Language:

English

Subjects (All):

Penn dissertations--Chemistry.

Chemistry--Penn dissertations.

Local Subjects:

Penn dissertations--Chemistry.

Chemistry--Penn dissertations.

Physical Description:

xxx, 216 pages : illustrations ; 29 cm

Production:

2009.

Summary:

Development of new mechanistic strategies and catalyst materials that activate substrates like CO, H2, CH4, C2H 4, O2, CH3OH, and water for the conversion of carbon monoxide, alkanes, and alkenes to organic oxygenates are central objectives encompassed by this thesis. Thermodynamic database for a wide scope of organo-metal transformations in a range of reaction media including benzene, water, and methanol has been continuously established in this thesis study.

Rhodium(II) tetramesitylporphyrin reacts as metalloradical with a wide variety of substrates to give diamagnetic products. Aliphatic C-H bonds are the preferred targets for activation by rhodium(II) porphyrins because of the steric effect of bulky porphyrin ligands. In the reaction, concerted C-H activation occurs through a four-centered transition state (Rh·---CR 3---H---·Rh) where two rhodium radicals work corporately to break the C-H bond. For methanol molecules which have both C-H and O-H bond, selective C-H and O-H activations have been achieved by simple adjustment on the reaction conditions. At low methanol concentrations ([CH3OH] < 0.1 M), two Rh(II) radicals accomplish the C-H activation to form equal amount of Rh-CH2OH and Rh-H. At high methanol concentrations ([CH3OH] > 0.5 M), methanol acts as donor ligand to induce the disproportionation of rhodium(II) to form rhodium(III) bismethanol cationic complex and rhodium(I) monomethanol anionic complex. Fast proton transfer occurs between these two species to form the neutral (CH3OH)Rh-OCH3 and (CH 3OH)Rh-H species as the O-H activation products. Upon standing, these products are slowly converted to C-H activation products (CH3OH)Rh-CH 2OH and (CH3OH)Rh-H that are more thermodynamically stable. Thermodynamic measurements on the equilibrium between rhodium(II), rhodium hydride, rhodium methoxide, and rhodium hydroxymethyl complexes predict approximate Rh-OCH3 bond dissociation enthalpy.

Both rhodium(III) aqueous and methanol solutions react with dihydrogen to produce rhodium hydride ([(TSPP)Rh-D(D2O)]-4, [(TSPP)Rh-D(CD3OD)]-4) which is in equilibrium with the rhodium(I) anion ([(TSPP)Rh1(D2O)] -5, [(TSPP)Rh1(CD3OD)]-5 ). Each of these rhodium porphyrin species functions as a precursor for a group of organometallic substrate reactions. Equilibrium thermodynamics have been investigated for these reactions, including the reactions of rhodium hydroxide and methoxide with olefins to produce beta-hydroxyalkyl and beta-methoxyalkyl complexes, reactions of rhodium hydride and olefins to produce rhodium alkyl complexes, and reactions of rhodium hydride with CO to produce rhodium formyl (Rh-CHO) complexes.

One of my research areas is the design and synthesis of diporphyrin ligands that form dimetal complexes capable of preorganizing transition states for substrate reactions that involve two metal centers. Dirhodium dimetalloradical diporphyrin complexes are observed to manifest large rate increases over mono-metalloradical activation reactions of hydrogen, methane, and other small molecule substrates. Therefore, in this study, new strategies for catalytic conversion of carbon monoxide to organic molecules have developed.

This dissertation also describes the mechanistic study on cobalt porphyrin mediated living radical polymerization of vinyl acetate. Formation of organo-cobalt complexes from cobalt(II) metalloradical during the induction period prior to polymerization involves both hydrogen abstraction from initiator radical by cobalt(II) radical followed by cobalt hydride addition to olefins, and coupling of cobalt(II) radical with monomer-based organic radicals. Fast radical exchanges among organo-cobalt complexes provide the control for producing large polymers with low-polydispersity. Associative mechanism has been identified as the low-energy pathway for radical exchange between vinyl acetate radicals and vinyl acetate-cobalt complexes. (Abstract shortened by UMI.)

Notes:

Adviser: Marsha I. Lester.

Thesis (Ph.D. in Chemistry) -- University of Pennsylvania, 2009.

Includes bibliographical references.

Local Notes:

University Microfilms order no.: 3363563.