Syntheses, chemistry and applications of organosilicon dianions, organogermanium dianions and pentacoordinate silicon compounds

This dissertation highlights the synthesis and chemistry of a new type of silole and germole dianions: 9-silafluorenyl dianion and 9-germafluorenyl dianion. These new dianions are synthesized from the reduction of corresponding dichlorides with potassium metal in refluxing THF or sodium/potassium alloy in THF at room temperature. The X-ray structures of both dianions show C-C bond length equalization in the five-membered silole rings and C-C bond length alternation in the six membered benzene rings, indicating aromatic delocalization of electrons in the metallole ring. The downfield 29Si chemical shift at 29.01 ppm also supports electron aromatic delocalization in the five-membered ring of silafluorenyl dianion.; Both dianions undergo nucleophilic substitutions, single-electron transfer reactions and radical reactions. Slow oxidation of the dianions by trace amounts of oxygen leads to formation of dimerized dianions. Heating the DME/hexane solution of silafluorenyl dianion in the presence of 18-crown-6 forms an unusual diradical dianion.; A novel pentacoordinate silicon compound with a pentalene structure is synthesized by slow solid-state oxidation from a methoxysilane containing a cyclopentadiene substituent. This pentacoordinate silapentalene forms pink crystals stable in air, and exhibits a remarkably bright orange fluorescence under white light. The X-ray crystal structure of the silapentalene shows a slightly distorted trigonal bipyramidal structure. The UV spectrum of the silapentalene has an intense absorption band at 526 nm (ϵ_max 2.16 × 104). The emission spectrum displays a peak at 554 nm with a quantum yield of 13%.; Silole and germole dianions are used for the reductive coupling of aryl aldehydes and ketones. The coupling reactions are carried out at −78°C in THF, very mild conditions compared with the reactions induced by metals and metal complexes in which room temperature or higher is required.; This dissertation describes the synthesis of the first polysilole polymer, in which every silicon atom in the polymer chain is also part of a silole ring. Several poly(silole-silane) copolymers are also synthesized and discussed. All of these polymers and copolymers are strongly fluorescent both in solutions and as solid films, emitting green or yellowish-green light (ϵ _max = 470–520 nm).