| Incompletely-condensed silsesquioxanes (e.g., ((c-{dollar}rm Csb6Hsb{lcub}11{rcub})sb7Sisb7Osb9(OH)sb3rbrack{dollar} (1)) have been studied as solution-state models for silica surfaces and as strong electron-withdrawing ligands for organometallic compounds. Their unique advantage for modelling silaceous surfaces stems from the presence of multiple silanol groups in close proximity to one another, similar to the hydrogen-bonded sites that exist on the surface of silica. The investigations into the reactivity of 1 have been useful in understanding why organometallic compounds, which often do not react with normal silanols or alcohols, react with the silica surface. Until recently, all polyhedral oligometallasilsesquioxanes (POMSS) formed when incompletely-condensed silsesquioxanes are reacted with organometallic compounds resulted in completely-condensed products--i.e., no free silanol groups were present. The major focus of this thesis involves the monofunctionalization of 1 to form silsesquioxane products which contain free silanol groups. The successful design of mono-anionic silsesquioxides (e.g., ((c-{dollar}rm Csb6Hsb{lcub}11{rcub})sb7Sisb7Osb{lcub}10{rcub}(OH)sb2rbracksp-{dollar} (2)) has allowed for the study of their reactivity with organometallic compounds. The results are very surprising, and in many cases lead to the formation of the same products which are observed when similar reactions are performed on the silica surface. The implications of these results with regards to silica surface chemistry are discussed.; As previously mentioned, incompletely-condensed silsesquioxanes have been useful as ligands for organometallic compounds. Until now, all chemical transformations of incompletely-condensed silsesquioxanes involved the formation of heterosiloxane (e.g., Si-O-P or Si-O-M) linkages from Si-OH groups. While many important--and sometimes, catalytically active--complexes have been synthesized via this route, the heterosiloxane linkages are often unstable to hydrolysis. Earlier attempts to form Si-halogen bonds--intermediates for stable Si-C bonds--resulted in decomposition of the silsesquioxane framework. Remarkably, the reaction of anhydrous HBF{dollar}sb4cdot{dollar}Me{dollar}sb2{dollar}O with 1 results in complete inversion of stereochemistry to afford exo-(c-{dollar}rm Csb6Hsb{lcub}11{rcub})sb7Sisb7Osb9Fsb3{dollar} (3) in quantitative yields. The details of this reaction as well as the subsequent transformations of 3 are discussed in this work and have opened a new chapter in silsesquioxane chemistry. |
