The synthesis and chemistry of silacyclobutadienes
Description
Silacyclobutadiene, the smallest member of sila (n) annulenes, is a strained and antiaromatic organosilicon species. The presence of a highly reactive Si=C bond as well as antiaromatic character renders it a synthetic challenge. In this work, the synthesis of two derivatives of silacyclobutadiene, their chemistry, and their mechanism of formation is described Chapter 1 provides a background on the silenes with emphasis on their synthesis, bonding, stability and reactivity. The effect of such a moiety in silacyclobutadiene is discussed. Subsequently, the theoretical studies on silacyclobutadiene and isomers are discussed. Lastly, two plausible synthetic approaches to the target molecule are provided Chapter 2 describes the synthesis of cyclopropenylaryltrisilanes as potential photochemical precursors to silacyclobutadiene. Crystal structures of the three cyclopropenylaryltrisilanes prepared with discussions on bond lengths and angles are included Chapter 3 presents the photochemical generation of cyclopropenylsilylenes from cyclopropenylaryltrisilanes in solution, and attempts to thermally transform them to the target molecule. Product identification and unravelling their mechanistic pathway by labelling studies is also elaborately presented Chapter 4 discusses the successful photochemical synthesis of silacyclobutadienes at 77K. In presence of chemical traps, stable silacyclobutenes are formed. In absence of trapping agents, tri-t-butylmesitylsilacyclobutadiene dimerizes to a novel disilacyclohexane. Contrastingly, tri-t-butyltri-isoprophenylsilacyclo butadiene reverts almost quantitatively to its cyclopropenylsilylene precursor. The crystal structure of methoxytrimethylsilane trapped silacyclobutadiene and of the dimer are also included Chapter 5 describes the successful attempts to prepare stable Dewarsilabenzenes by trapping of the silacyclobutadienes with acetylenes Chapter 6 presents the mechanistic studies performed to determine the path of rearrangement of cyclopropenylsilylenes to silacyclobutadienes with the use of a different group on the cyclopropenyl ring. From the ratio of isomeric silacyclobutadienes trapped, the mode of rearrangement has been determined Chapter 7 describes the efforts made to prepare silacyclobutadienes from cyclopropenylsilylenium ions. The experiments suggest this route to be synthetically viable The successful synthesis of silacyclobutadienes is another addition to the class of (4) annulenes which already consists of the extensively studied cyclobutadiene, and azacyclobutadiene. With continuing investigations on other derivatives of silacyclobutadiene, insightful comparison with the already known species can be made