Trichlorosilane anchor

In one example, polystyrene sulfonate (PSS) brushes terminated with trichlorosilane anchor groups are attached both to spherical [51] and to planar silicon oxide surfaces [52-54]. To obtain such structures in the first step a monolayer consisting of neutral polystyrene molecules is formed by reaction of the silane anchor groups with silanol groups on the silicon/silica substrates. The neutral polymer is then transformed into the polyelectrolyte in a second step via a polymer-analogous sulfonation reaction. The thus ob-... 

Patterns of ordered molecular islands surrounded by disordered molecules are common in Langmuir layers, where even in zero surface pressure molecules self-organize at the air—water interface. The difference between the two systems is that in SAMs of trichlorosilanes the island is comprised of polymerized surfactants, and therefore the mobihty of individual molecules is restricted. This lack of mobihty is probably the principal reason why SAMs of alkyltrichlorosilanes are less ordered than, for example, fatty acids on AgO, or thiols on gold. The coupling of polymerization and surface anchoring is a primary source of the reproducibihty problems. Small differences in water content and in surface Si—OH group concentration may result in a significant difference in monolayer quahty. Alkyl silanes remain, however, ideal materials for surface modification and functionalization apphcations, eg, as adhesion promoters (166—168) and boundary lubricants (169—171). 

More recently, in organocatalysis, Kocovsky [69] has reported asymmetric reduction of imine with trichlorosilane catalyzed by an (A-methylvaline)-derived formamide anchored to a polymer. Under the best conditions, with 15 mol% of the catalyst enantiomeric excesses were about 85% and the catalyst could be reuse. 

Phenyl trichlorosilane, CeHsSiCU, reacts quantitatively with dry silica gels and the amount irreversibly reacted with the silanol surface permits estimation of surface area. There are 2.16 phenyl groups anchored to the surface per square nanometer (3.6 micromoles m" ) (94). 

In order to enable the isolation procedure of the organocatalysts, Kocovsky s group also reported an alternative approach using a dendron-anchored organocat-alyst 103 to efficiently reduce the imines with trichlorosilane 2 [209]. The isolation procedure of the catalyst from the crude was substantially simplified, since most of the catalyst (>90 %) could be recovered by precipitation and centrifugation (Fig. 10). 

Maikov AV, Figlus M, KoCovsky P. Polymer-supported orga-nocatalysts asymmetric reduction of imines with trichlorosilane catalyzed by an amino acid-derived formamide anchored to a polymer. J. Org. Chem. 2008 73 3985-3995. 

---