An efficient convergent synthesis of novel anisotropic adsorbates based on nanometer-sized and tripod-shaped oligophenylenes end-capped with triallylsilyl groups

This article describes an efficient and convergent synthesis of a novel tripod-shaped oligophenylene compound. The compound consists of three oligophenylene heptamers as the tripod legs and one bromophenyl group as the functional arm, joining at a tetrahedron silicon atom. Each tripod leg is end-capped with a triallylsilyl group for covalently anchoring the molecules on hydrogen-terminated silicon surfaces via hydrosilylation. The compound may represent a new type of anisotropic adsorbates for controlling the orientation of and spacing between functional groups in organic thin films and nanostructures grown on silicon surfaces. An oligophenylene hexamer end-capped with a triallylsilyl group and a pinacol arylboronate group was readily derived from diiodoterphenyl with a bromophenyl boronic acid by selective Suzuki coupling. Reaction conditions for highly selective Suzuki coupling of sterically hindered pinacol boronate with aryl iodide in the presence of multiple ethenyl groups for the competing Heck reaction were developed. Under the optimal conditions (Pd(PPh3)(4)/KOH/Bu4NBr/toluene/H2O, 85 degreesC, overnight), p-bromophenyl-tris(p-iodo-phenyl)silane reacted with 3 equiv of the hexaphenylene boronate to provide the tripod-shaped oligophenylene, composed of 22 phenylene and 9 allyl groups, in 78% yield.