Thienyl- and furylborane oligomers, polymers, and macrocycles - dvelopment of a catalytic Si/B exchange reaction as a novel B-C bond formation method

The synthesis of new functional materials with tailored optical and (electro)chemical properties is of considerable interest in current research. State-of-the-art inorganic-based devices rely on available resources and are limited by poor processability. Due to the better processability and potential use in light-weight devices, organic materials have emerged as a very promising alternative to currently used inorganic materials. Organic polymers have been the subject of tremendous research activity in the last decades. They found application in organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). An effective way to tune the optical and electronic properties of these materials beyond that is based on the incorporation of electron-acceptor and electron-donor moieties into organic structures, thus, giving rise to π interactions between them. Based upon its inherent electron deficiency, incorporation of boron into organic π systems inherits the possibility of obtaining materials with unique and improved properties compared to their purely organic congeners.In this thesis, a novel, environmental benign and highly efficient synthetic method for the formation of B–C bonds via Si/B exchange is presented. The catalytic reaction proceeds smoothly and selectively at ambient temperature, affording poly(2-thienyl)- and poly(2-furyl)boranes amongst other (hetero)arylboranes. In order to investigate the optical properties upon extension of the π system, the new synthetic protocol has been employed on the synthesis of monomeric, dimeric and trimeric model compounds. This allowed to determine the effective conjugation wavelength of the thiophene- and furan-based materials. In addition, suitable organoborane (macro)molecules can serve as potent chemical sensors for the selective detection of fluoride anions. We performed first mechanistic studies on this catalytic approach, which reveal a linear relation between the reaction rate and the amount of catalyst applied and the total concentration of the reaction mixture. The dependency of the reaction progression on the nature of the starting materials was found to be complex. This is presumably a result of two different reaction paths leading to the desired product. The influence of the kinetically stabilizing aryl group (which provides stability to the Lewis acidic boron center towards air and moisture) and the substitution pattern at the 5,5´-positions of di(2-thienyl)arylboranes on the structure in the solid-state has been verified. Furthermore, a novel tetrathiatetraboraporphyrinogen was successfully synthesized, which is formally derived from the porphyrin framework by substitution of pyrrole with thiophene and the meso carbon atoms by boron. The resulting 16 π electron species comprises a fully delocalized system with unique absorption and emission behavior, compared to its linear congener. Upon addition of fluoride anions, its UV–vis absorption and fluorescence emission characteristics are influenced significantly. Therefore, it also serves as a potent chemical sensor. Finally, the first P–B–P bridged [3]ferrocenophane with a redox trigger has been synthesized. An intramolecular electron transfer process from the bridge to the ferrocenium backbone in the mono-oxidized state is supported by electrochemical investigations