Iron catalysts for the epoxidation of olefins and C-C Cross coupling

Hasan, Kamrul (2012) Iron catalysts for the epoxidation of olefins and C-C Cross coupling. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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    Available under License - The author retains copyright ownership and moral rights in this thesis. Neither the thesis nor substantial extracts from it may be printed or otherwise reproduced without the author's permission.
    (Original Version)

Abstract

This thesis describes the synthesis, structure and catalytic activity of aminebis(phenolate)Fe(llI) complexes. Fe(III) halide complexes were synthesized supported by tetradentate amine-bis(phenolate) ligands. The general formulae of these ligands are abbreviated as [O₂N₂]RR’ and [O ₂NO’]RR’R”, where [O₂N₂] and [O₂NO’] to describe the four donor atoms of the ligands, R and R'('Bu or Me) represent the substituents at the 2-and 4- positions on the phenolate rings and R" defines the pendant donor functionality such as methoxyethyl (Meth) or tetrahydrofurfuryl (Furf). These paramagnetic complexes were characterized by a variety of methods including elemental analysis, MALDI-TOF mass spectrometry, UV-vis spectroscopy, and magnetic moment measurements. Three iron complexes, FeCl[O₂N₂]BuBu (1), FeBr[O₂N₂]BuBu (2) and FeBr[O₂NO’]BuMeMeth (3) were structurally characterized by single crystal X-ray diffraction. Magnetic moment measurements of these complexes show high-spin d⁵ Fe(lll) centers. Also, variable temperature magnetic susceptibility measurements of the three structurally characterized complexes were conducted using a SQUID magnetometer. -- For epoxidation of olefins, H₂O₂ was chosen as terminal oxidant because it is convenient and produces water as a by-product. The catalytic activity of these aminebis(phenolate)Fe(III ) halide complexes were investigated for the epoxidation of trans-stilbene. The complex FeCl[O₂N₂]BuBu (1) gave modest yield (36%) of trans-stilbene oxide after 19 h stirring of the reaction mixture at 25°C. However, a practical method for the epoxidation of olefins was discovered by the combination of FeCl₃·6H₂O and 1-methylimidazole in acetone. Heating the reaction mixture to 62°C for 19-21 h significantly improved the product yields. The optimized catalytic conditions were applicable for both aromatic and aliphatic internal and terminal olefins. Also, in-situ generated Fe(III) complexes, made by adding to FeCl₃·6H₂O solutions of selected amine-bis(phenol) ligands, were investigated for the epoxidation of trans-stilbene to see whether any enhancement of reactivity could be obtained. Tridentate amine-bis(phenol) ligands (abbreviated H₂[O₂N]RR’) improved the product yields up to 64% but these yields were less than the epoxidation activity (93%) while using FeCl₃·6H₂O and I-methylimidazole alone. -- Finally, six amine-bis(phenolate)Fe(IlI)(acac) (acac = acetylacetonate) complexes were synthesized by employing previously reported tetradentate amine-bis(phenolate) ligands including [O₂NN’]RR’R”, where R” is the pendant donor functionality such as N,N-dimethylaminoethyl (NMe2). These paramagnetic complexes were also characterized by a variety of methods including elemental analysis, MALDI-TOF mass spectrometry, UV-vis and lR spectroscopy, cyclic voltammetry, and magnetic moment measurements. Four of these complexes, Fe(acac)[O₂N₂]BuBu (9), Fe(acac)[O₂NN’]BuBuNMe2 (10), Fe(acac)[O ₂NN’]BuMeNMe2 (11), and Fe(acac)[O₂NO’]BuMeMeth (13) were structurally characterized by single crystal X-ray diffraction. Magnetic moment measurements of these complexes indicate high-spin d⁵ Fe(III) centers. Cyclic voltammetry of these complexes show ligand-centered reversible redox processes. Preliminary catalytic activity of these complexes was investigated for the C-C cross-coupling of aryl Grignard reagents with alkyl halides. Secondary cyclic halides such as cyclohexyl chloride and bromides gave high yields, however, benzyl chloride and bromide gave moderate and acyclic 2-chloro- and 2-bromobutanes gave poor yields of cross-coupled product.

Item Type: Thesis (Doctoral (PhD))
URI: http://research.library.mun.ca/id/eprint/6118
Item ID: 6118
Additional Information: Includes bibliographical references.
Department(s): Science, Faculty of > Chemistry
Date: 2012
Date Type: Submission
Library of Congress Subject Heading: Epoxy compounds; Aklenes; Iron catalysts; chemical reactions

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