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Synthesis of New Organometallic Polymers via Ring-Opening Polymerization of Strained Ferrocenophanes Containing Group 13, 14, or 15 Elements in Bridging Positions



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The presence of transition metals in the main chain of synthetic polymers can give rise to unique properties which differ from those of organic polymers. Recently, our group developed a route to strained ferrocenophanes (FCPs) with planar chirality. Through ring-opening polymerization (ROP) of these chiral monomers, new metallopolymers with potentially interesting properties could be obtained. In addition, the chirality of [1]FCPs provided some insight into the mechanism of a ROP process. Following known “Ugi’s amine” chemistry, new dibromoferrocene derivatives with planar-chirality were prepared. The synthesis and characterization of two families of dibromoferrocene derivatives with C2 and C1 symmetry, respectively, are described. Dibromoferrocene derivatives (Sp,Sp)-1,1'-dibromo-2,2'-di(3-pentyl)ferrocene [(Sp,Sp)-107] and (R,R,Sp,Sp)-1,1'-dibromo-2,2'-di(2-butyl)ferrocene [(R,R,Sp,Sp)-108] with C2 symmetry were prepared and fully characterized. The molecular structure of (Sp,Sp)-107 was determined by single-crystal X-ray analysis. The synthesis and characterization of 1,1'-dibromo-2-isopropylferrocene (109) with C1 symmetry is reported in racemic (rac-109) as well as in enantiomerically pure form [(Sp)-109]. Salt-metathesis reactions of the dilithio derivative of (Sp,Sp)-107 with ArʹGaCl2 [Arʹ = 2-(Me2NCH2)C6H4] and Me2SiCl2 afforded novel gallium- and silicon-bridged [1]FCPs (Sp,Sp)-124 and (Sp,Sp)-125, respectively. Salt-metathesis reaction of the dilithio derivative of rac-109 and (Sp)-109 with Me2SiCl2 affords novel silicon-bridged [1]FCPs in both racemic and enantiomerically pure forms [rac-126 and (Sp)-126]. The molecular structure of rac-126 was determined by single-crystal X-ray analysis. Salt-metathesis reaction of the dilithio derivative of (Sp,Sp)-107 with tBuPCl2 yielded new phosphorus-bridged [1]FCPs (127). Compound 127 with C1 symmetry [(Sp,Sp)-127C1] isomerized in reaction mixture to give the Cs-symmetrical phosphorus-bridged [1]FCP meso-127Cs. The molecular structure of meso-127Cs was determined by single-crystal X-ray analysis. DFT calculations were performed to study the structure and understand the extra strain in (Sp,Sp)-127C1. The salt-metathesis reaction of the dilithio derivative of rac-109 and PhPCl2 afforded a mixture of cis and trans isomers of a phosphorus-bridged [1]FCP (rac-130), each present as a racemate. Experimental and theoretical data for the interconversion of cis and trans diastereomers of rac-130, which occurs through inversion at phosphorus, is reported. The molecular structure of the cis isomer rac-130cis was determined by single-crystal X-ray analysis. Differential scanning calorimetry (DSC) thermographs of rac-126, (Sp)-126, and rac-130 suggest that these are potential candidates for thermal ROP. Compounds rac-126 and (Sp)-126 were polymerized via thermal ROP and afforded polymers 132 and 133, respectively. The resulting polymers were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR) spectroscopy, and carbon-hydrogen-nitrogen (CHN) elemental analysis. The high molecular weight and low polydispersity index (PDI) were determined by triple-detection GPC analysis for polymers 132 and 133. The thermal ROP of silicon-bridged [1]FCP with iPr groups on both Cp rings resulted in polymer 134 which due to solubility issues could not be fully characterized. Thermal ROP of rac-130 was performed and the resulting products were sulfurized for characterization. This ROP afforded both linear polymer (135) and several cyclic phosphines as side products. Polymer 136 was analyzed by GPC, NMR spectroscopy, and CHN analysis. Mass spectra of this mixture revealed the presence of cyclic phosphines from dimers to heptamers. Preparative thin layer chromatography (PTLC) was carried out in order to separate this mixture. Suitable crystals of three different dimers for X-ray analysis were obtained for complete structure determinations.



Organometallic Polymers, Ring-Opening Polymerization, Strained Ferrocenophanes



Doctor of Philosophy (Ph.D.)






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