Graduation Year

2014

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Chemistry

Major Professor

Michael J. Zaworotko

Keywords

chiral induction, chirality, chiral resolution, crystal structure, metal-organic frameworks, phase transformation

Abstract

Owing to the growing demand for enantiopurity in biological and chemical processes, tremendous efforts have been devoted to the synthesis of homochiral metal-organic materials (MOMs) because of their potential applications in chiral separation and asymmetric catalysis. In this dissertation, the synthetic strategies for homochiral MOMs are discussed keeping the focus on their applications. Two distinct approaches have been taken to synthesize chiral structures with different topologies and accessible cavities. The chiral MOMs have been utilized in enantioselective separation of racemates.

Chiral variants of the prototypal metal-organic framework MOF-5, δ-CMOF-5 and [lambda]-CMOF-5, have been synthesized by preparing MOF-5 in the presence of L-proline or D-proline, respectively. CMOF-5 crystallizes in chiral space group P213 instead of Fm-3m as exhibited by MOF-5. The phase purity of CMOF-5 was validated by single crystal and powder X-ray diffraction, IR spectroscopy, TGA, N2 adsorption, microanalysis and solid-state CD. CMOF-5 undergoes a reversible single crystal to single crystal phase change to MOF-5 when immersed in a variety of organic solvents although N-methyl-2-pyrolidone, NMP, does not induce loss of chirality. Indeed, MOF-5 undergoes chiral induction when immersed in NMP, affording racemic CMOF-5.

A pair of homochiral network materials (CNMs), [Co2(S-man)2(bpy)3](NO3)2·guests (1S) and [Co2(R-man)2(bpy)3](NO3)2·guests (1R) based upon S-mendelic acid and R-mendelic acid were synthesized and characterized, respectively. The cationic networks contain 1D homochiral channels with the cross section of 8.0 Å × 8.0 Å. The chiral amphiphilic channel surfaces lined with hydrophilic nitrate anions and hydrophobic phenyl groups are capable for multiple interactions with guest species. Chiral resolution of 1-phenyl-1-propanol (PP) enantiomers was performed utilizing the homochiral porosity of 1S and 1R through different time period at different temperatures with/without additives. The mechanism for enantioselective separation of PP was fully investigated through single crystal structural analysis of guest exchanged 1S and 1R. Chiral resolution of PP revealed enhanced performance with additive, which can significantly improve the ee value from 32% to 60%.

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