Transition metal catalyzed silane alcoholysis in a highly polar solvent-application to monosaccharides and polyols
This thesis is an investigation of transition metal catalyzed silane alcoholysis reactions of monosaccharides and alcohols. In a model study using ethylene glycol and triethylsilane, several homogeneous and heterogeneous catalysts including a newly discovered dimeric complex Ru2([mu]-Cl) 2Cl2(CO)4(PMe3)2 ( 1) have been shown to be active for silane alcoholysis in a highly polar amide solvent. The dynamic solution behaviour and the structure of the complex 1 as determined by single crystal X-ray structure analysis are reported. In the silylation of monosaccharides using silane alcoholysis, an 'in situ' generated palladium nanoparticle colloid that was discovered in the course of this study has been employed for the first time. The method allows a convenient access to mono/di-silylated sugars that are either produced only as minor components or not at all by the established silyl chloride method. The regioselectivity and mechanism of the palladium nanoparticle catalyzed silane alcoholysis reaction have been investigated. The silane alcoholysis of sugars with homogeneous catalysts derived from [M(COD)(PPh 3)2]+SbF6- (M = Ir, Rh) produce di-/tri-silylated derivatives with only one free hydroxyl function in one step. The isolated yields of these derivatives exceed those of any known synthetic methods. In a concurrent study that tested the scope and limitation of the palladium nanoparticle catalyzed silane alcoholysis, a new cross-coupling reaction generating Si-S bonds via an unusual Csp2-S bond activation was discovered. The new cross-coupling reaction gives access to synthetically useful organosilathianes and silathio-glycosides, a new class of compounds in carbohydrate chemistry.