A Flexible Approach to [1]Ferrocenophanes: Metallopolymers through a New Family of Chiral Sandwich Compounds
Date
2014-11-25
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Thesis
Degree Level
Doctoral
Abstract
Applying known “Ugi’s amine” chemistry and based on a literature procedure, (R,R,Sp,Sp)-2,2′-bis(α-N,N-dimethylaminoethyl)-1,1′-dibromoferrocene was prepared and the pathway was modified for a synthesis on a larger scale. Adding two more synthetic steps, amino groups were replaced with methyl groups which resulted in the planar-chiral (Sp,Sp)-1,1′-dibromo-2,2´-di(isopropyl)ferrocene (120). Starting with 120, lithium-bromine exchange using nBuLi and different solvent systems was investigated and a reliable method was developed. Salt-metathesis reaction of (Sp,Sp)-1,1'-dilithio-2,2´-di(isopropyl)ferrocene (121) and Ar′GaCl2 [Ar′ = 2-(Me2NCH2)C6H4] was performed and yielded the respective [1]ferrocenophane ([1]FCP) 122 with high conversions. This gallium-bridged [1]FCP 122 was isolated by crystallization from the reaction mixture and its molecular structure in the solid state was determined. The Differential Scanning Calorimetry (DSC) thermograph of the gallium-bridged [1]FCP 122 proved that the [1]FCP is a potential candidate for thermal ring-opening polymerization (ROP). The starting compound Ar′InCl2 was reacted with 121 and yielded a mixture of an indium-bridged [1]FCP (1261) and a [1.1]FCP (1262). Reacting the bulkier reagent (Mamx)InCl2 [Mamx = 2,4-tBu2-6-(Me2NCH2)C6H2] with 121 resulted in the selective formation of an indium-bridged [1]FCP (1251). All attempts to isolate the strained indium-bridged [1]FCP were unsuccessful as it reacted further through a spontaneous ROP under conditions of its formation. DFT (Density Functional Theory) calculations were performed to investigate the structure and reactivity of synthesized indium-bridged [1]FCPs. Moreover, the effects of different substituents on the unusual reactivity of indium-bridged [1]FCP was studied.
A group of amino(dichloro)boranes with different substitutions [Et2NBCl2, iPr2NBCl2, and tBu(Me3Si)NBCl2] were reacted with 121 and its 3-pentyl substituted analog [(Sp,Sp)-1,1′-dilithio-2,2′-di(3-pentyl)ferrocene] (131). Six bora[1]ferrocenophanes were synthesized and purified with different techniques including crystallization, sublimation, and flask-to-flask condensation. While salt-metathesis reactions with Et2NBCl2 were very selective toward [1]FCPs, employing the amino(dichloro)boranes iPr2NBCl2 and tBu(Me3Si)NBCl2 resulted in formation of significant amounts of bis(boryl)ferrocenes as byproducts. A systematic study was performed, which resulted in increasing the reaction temperature and controlling the rate of addition of the amino(dichloro)boranes to increase the yield of desired [1]FCPs. Thermal ROP of selected bora[1]FCPs were performed and the resulting polymers were analyzed by Gel Permission Chromatography (GPC) and Dynamic Light Scattering (DLS).
Synthesis of chiral group-14-bridged [1]FCPs were attempted by salt-metathesis reaction of 121 with tBuSnCl2 and Me2SiCl2. The respective strained [1]FCPs (140 and 141) were formed in the reaction mixture quantitatively and isolated by vacuum sublimation in good yields. The molecular structures in the solid state of both [1]FCPs were determined and it was deduced that an interaction between alkyl groups increased the strain in the molecules. Measuring DSC thermographs proved these compounds to be suitable for thermal ROP.
A group of chiral phosphorus-bridged [1]FCPs (142, 143 and 144) with different groups in the bridging position (Ph, iPr, and tBu) were prepared by reacting 121 with the respective phosphorus dihalides. These compounds were stable enough to be purified by column chromatography. The molecular structures of isopropyl and phenyl substituted phosphorus-bridged [1]FCPs were determined in the solid state. Potential application of these phosphorus-bridged [1]FCPs as monodentate ligands for asymmetric catalysis will be studied in the future.
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Keywords
[1]ferrocenophanes, Ring-opening polymerization, Metallopolymers,
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Chemistry
Program
Chemistry