Synthesis and Reactivity of molecular Silicas with and without Oxygen Defects and Their Chalcogen Analogues
Final Report Abstract
The controlled synthesis of non-stoichiometric silicon oxides, specifically SixOy (where y<2x), known as silicon suboxides or oxygen-deficient silicas, is a crucial pursuit owing to their diverse applications and the pivotal role played by silicon suboxides, such as silicon monoxide, as semiconducting layers or interlayers in electronics. This project was predominantly dedicated to pioneering non-hydrolytic synthetic methods aimed at creating well-defined molecular models featuring SixOy (y<2x) to enhance our understanding of the structures and chemical properties of oxygen-deficient silica. Three strategies were devised to achieve these well-defined molecular model compounds. (i) Commencing with the xanthene-bridged N-heterocyclic silylene-supported silicon(0) complex (silylone), we isolated two novel silicon oxide complexes containing Si6O2 and Si6O4 with Si-Si bonds through controlled oxygenation with N2O in diethyl ether, respectively. (ii) Recognizing the facile activation of small molecules by silylenes and their metal-free transformation of molecules such as O2, N2O, CO2, and CO into organic substrates, our focus shifted to constructing molecular SixOy compounds as silica molecular models directly from bis-silylenes and related species. This not only enabled the realization of numerous molecular models with varying silicon and oxygen ratios but also expanded our silylene chemistry to inert chemical bond activation, yielding unconventional silicon-containing materials. This was facilitated by the cooperativity of the two silicon(II) centers in the bis-silylenes. For instance, the two preorganized silylene centers can coordinate the inert CO, mimicking a transition metal for further CO bond activation. (iii) Perchlorinated cyclopentasilane Si5Cl10 and cyclohexasilane Si6Cl12 with Si5 and Si6 rings underwent alcoholysis with silanols, emerging as suitable precursors for producing another type of molecular models of silicas. This approach provided a superior route to silicon suboxides with oxygen defects and Si-Si bonds. Various silicon suboxide models were successfully synthesized and fully characterized, intended for comparative analysis with silicon suboxide units present in silica. Moreover, a novel synthesis route for a new type of silicon monoxide materials was established. Controlled thermolysis of a silicon suboxide model, resulting from alcoholysis of perchlorinated cyclohexasilane Si6Cl12 with half of the chlorine substituents in the molecule, led to the desired new silicon monoxide, eliminating the volatile ClSi(iPr)3 during heating. The resulting SiO products underwent comprehensive characterization, offering valuable insights into their properties. Notably, the yellow silicon suboxide material obtained shows promise as an anode material for lithium-ion batteries. In comparison with the known k-SiO, which contains silicon and silicon dioxide clusters, the new silicon monoxide is composed uniformly of silicon monoxide clusters. The use of this silicon monoxide material could yield superior results in lithium-ion batteries. Furthermore, a novel Si(II)-network with SiOH functionalities was developed by another non-hydrolytic sol-gel method with perchlorinated cyclohexasilane Si6Cl12 followed by calcination. These silanol groups can be used for grafting of a metalorganic platinum complex, which was also successfully tested for catalytic hydrogenation reactions with alkenes and alkynes.
Publications
-
Beiträge zur Chemie neuer Modellverbindungen für Silica mit Sauerstoffdefizit, Ph.D. Dissertation
Paulmann, J.
-
Beiträge zur Immobilisierung metallorganischer Komplexe, Ph.D. Dissertation
Czerny, F.
-
Homocoupling of CO and isocyanide mediated by a C,C′-bis(silylenyl)-substituted ortho-carborane. Chemical Communications, 56(5), 747-750.
Xiong, Yun; Yao, Shenglai; Szilvási, Tibor; Ruzicka, Ales & Driess, Matthias
-
Isolable Dibenzo[a,e]disilapentalene with a Dichotomic Reactivity toward CO2. Journal of the American Chemical Society, 142(40), 16935-16941.
Su, Bochao; Kostenko, Arseni; Yao, Shenglai & Driess, Matthias
-
Distinctly different reactivity of bis(silylenyl)-versus phosphanyl-silylenyl-substituted o-dicarborane towards O2, N2O and CO2. Chemical Communications, 57(48), 5965-5968.
Xiong, Yun; Yao, Shenglai; Ruzicka, Ales & Driess, Matthias
